When we talk about the end of the cosmos, one idea appears again and again: the Big Crunch or Great CollapseAccording to this proposal, the expanding universe would eventually slow down, reverse its direction, and contract until it reaches an extreme state. This is not just any fantasy, but a cosmological possibility which has been studied for decades, supported by the same tools we use to describe the Big Bang.
In recent years, this hypothesis has experienced a small revival: some studies have suggested that the expansion may not be eternal and that, under certain conditions regarding the dark energythe cosmic rhythm would reverse. There are even models that venture specific time windows for the start of the contraction, which has reopened the debate and led many to wonder if the end of the universe will come from a collapse and not from endless cooling.
What is the Big Crunch: From the Big Bang to the Great Collapse
The Big Crunch, also called Great Implosion or Great CollapseIt proposes a fate opposite to the Big Bang: if the universe emerged from a dense, hot state and began to expand, there could come a time when the expansion stopsgravity prevails and all the contents of the cosmos begin to approach each other again, compressing to an extreme state, perhaps a space-time singularity.
This vision is the symmetrical counterpart of the proposal of Big BangThe universe expands, slows down, reverses its sign, and collapses. In that scenario, distant objects would experience a marked blue shift as they approach; in some older popular science sources this effect is mentioned with non-standard names such as the "Tudón effect", but what is relevant is the shift towards more energetic frequencies as the contraction get moving.
The theoretical basis: general relativity, Friedmann, Lemaître and company
The possibility of predicting cosmic destiny arises with the Einstein's general relativity (1915)His equations, applied to the universe as a whole, allow for multiple solutions. In the 1920s, Alexander Friedmann y Georges Lemaitre They showed expanding solutions, and shortly after Edwin hubble He observed (from Cepheid variables in distant galaxies) that the universe, in fact, it expandsbroadening the vision of observable universe.
Einstein introduced a cosmological constant with the idea of maintaining a static universe; after Hubble's discovery, he regretted that adjustment. Decades later, with the distant supernovae of 1998The observations were interpreted as an expansion that not only continues but it accelerates, which reintroduced the cosmological constant (or something equivalent) as dark energy: a negatively pressured ingredient that dominates the energy budget.
A practical way to organize potential destinations is the parameter Ω (Omega), which compares the average density of the universe with the critical density: if Ω is greater than, less than or equal to 1, the universe turns out closed, open o map respectively, with different overall geometric consequences (triangles that add up to more than 180 degrees in the closed one, less than 180 in the open one, exactly 180 in the plane; parallels that end up meeting, that diverge or that remain equidistant).
- Closed universe (Ω>1)With little or no dark energy, gravity can slow the expansion and cause a contraction In short, opening the door to the Big Crunch. If dark energy dominates, however, continued expansion could occur despite the closed geometry.
- Open universe (Ω<1)Even without dark energy, it expands forever; with dark energy, the expansion not only continues but it accelerates, tipping the scales towards endings like the Big Freeze or the Big Rip.
- Flat universe (Ω=1)Without dark energy, the expansion would be eternal but slowed, asymptotically approaching zero; with dark energy, the universe accelerates and heads towards an end by cooling or disintegration.
The current consensus among many cosmologists is that final destiny depends on the global shape of space and, above all, the behavior of the dark energyAlthough there are minority models (for example, 2005 proposals on a fermion-boson fate with Bose-Einstein condensates (on a large scale) that explore alternative scenarios, the key remains to measure accurately densities, expansion rates and their evolution.
When might a contraction occur? Proposed dates and scenarios
Two striking lines of thought have emerged in recent publications. On the one hand, there was an echo of Princeton researchers publishing in PNAS who spoke of signs consistent with a possible accelerated future contractionThis would make the Big Crunch closer than expected. These results were interpreted as a plot twist regarding constant dark energy.
On the other hand, an international study led by the Cornell University along with the International Physics Centre of Donostia and Shanghai Jiao Tong University, disseminated in arXiv, explores a model in which dark energy would not be fixed but dynamicUnder that hypothesis, the expansion would slow down and reverse in about 7.000 billion years, and the total collapse would arrive approximately 13.000 billion years later, completing a Big Bang–Big Crunch cycle of about 33.000 billion.
Other published estimates suggest a contraction within a timeframe of about 20.000 million yearsOn a human scale it sounds like science fiction, but on a human scale cosmic It's relatively "early" if we remember that the universe is around 13.800 billion years old. In any case, it's about colors that compete with the still dominant scenario of eternal expansion and that depend on how dark energy evolves.
Does the Big Crunch conflict with the second law of thermodynamics?
A common question is whether a collapse towards a singularity “violates” the second law, since the entropy of an isolated system shouldn't decreaseThe short answer is that the Big Crunch does not necessarily imply lower entropy: gravitation opens up new degrees of freedom (formation of structures, collapse, black holes) and, in fact, the black holes These are objects with enormous entropy. The total entropy can continue to grow even during a contraction phase.
In observable terms, a global contraction would imply that radiation from distant galaxies would be displaces blue, increasing its apparent energy, while the average density of the universe increases. That is, it is not that the cosmos “orders” its contents by reducing entropy; rather, the process of gravitational contraction It generates states with greater gravitational disorder, consistent with the second law. This point is highly technical, but it dismantles the idea that the Big Crunch is "absurd" for thermodynamic reasons.
The bounce: from the Big Crunch to the Big Bounce
Some theoretical frameworks, such as the Loop Quantum Gravity Driven by Abhay Ashtekar, they suggest the possibility of a Big BounceWhen the density reaches extreme values, quantum effects of the geometry would prevent the singularity and cause a rebound, initiating a new expansionIn this scenario, the universe alternates between phases of expansion and contraction in a potentially endless sequence.
The classic version of oscillating universe However, this clashes with the second law: with each oscillation, entropy increases, making it difficult to return to a state "equal" to the previous one. Some modern ideas, such as the cyclic brane modelsThey have attempted to circumvent this problem by allowing expansion to dilute the accumulated entropy before a new cycle. These are suggestive proposals, but still speculative.
There are also more exotic approaches, such as the multilevel cosmological modelwhich imagines infinite levels of universes with their own beginnings and ends, while the overall whole would have infinite existence. As of today, they are theoretical scenarios without direct observational support.
Other endings on the table: Big Freeze, Big Rip, fake vacuum…
If dark energy persists and geometry is flat or open, the most popular destination is the Big Freeze or heat death: the expansion continues forever, the stars die out on timescales of around one billion years, galaxies end up dominated by black holes that, with unimaginably long times, they evaporate due to Hawking radiation.
In some grand unified theories, the protons They would decay, transforming the interstellar gas into pairs of electrons and positrons that eventually annihilate each other. photons and leptonsThe universe would end up as an increasingly cold and diluted radiative soup, with energy progressively shifting towards the red end due to expansion.
Taking acceleration to the extreme, the following appears: Big ripDark energy would overcome not only gravity, but also the forces electromagnetic already weak nuclear bonds, tearing apart galaxies, stars, planets and, ultimately, matter itself.
Another speculative outcome is the vacuum metastabilityIf our quantum vacuum were false (not the lowest energy state), a “truer” vacuum bubble could be formed that would advance rewriting the physical constants and the very structure of matter. It would be a silent but devastating end for the laws of physics as we know them.
In absurdly long horizons, some authors, such as Sean Carroll and Jennifer Chen, have discussed the small possibility that the quantum fluctuations produce new Big Bangs within a thermal sea, with chilling times on the order of 10101056 years. The theorem of also comes into play Poincaré and thermal fluctuations to imagine “recurrences” of cosmological order.
How it's decided: by weighing the universe
The choice between these endings is addressed by measuring the relative contribution of materialradiation, dark matter, and dark energy at critical density, and checking the scenarios against data from Type Ia supernovaegalaxy clusters and the anisotropies of the cosmic microwave background. Broadly speaking, much data today is compatible with a universe map and dominated by dark energy, which tips the scales towards the Big Freeze, without ruling out nuances about the dynamic of that dark energy.
The place of religion, culture, and science fiction
Virtually all major religions have narratives about the end of the worldThe theological study of these visions is known as eschatologyOften, these accounts have been reinterpreted in light of scientific advances, avoiding literal readings of expressions like "the stars will fall from the sky," which reflect ancient understandings of the heavens.
Popular culture has made the end of the universe fertile ground. In literature, the story of Isaac Asimov, The Last Question (heat death and computational rebirth), the novel Tau Zero by Poul Anderson (cyclical universe with Big Crunch followed by a new Big Bang), the narrative poem A Long Time Dying by Geoffrey A. Landis, or The Big Chill by Alan Moore, where a superhero witnesses cosmic cooling. There are also forays like The World at the End of Time by Frederik Pohl.
Humor and satire have done their part: the restaurant Milliways, The Restaurant at the End of the Universe Douglas Adams's work allows us to contemplate the ending as a spectacle; Woody Allen included in Annie Hall the joke about the child worried about the expansion of the universe.
In television and film, there's everything: Red Dwarf It speculates on a time that “goes backwards” in a cosmos that is heading towards the Big Crunch; Lexx Imagine a contraction caused by a legion of mechanical arms; Star Trek: Deep Space Nine He addresses the topic in “Chrysalis”; Plan 9 from outer space uses the threat of destroying the universe; Doctor Who It features a “vacuum ship” sphere capable of surviving a cycle cyclic.
Anime is also making an appearance: eureka 7 It postulates a limit of “biological density” that triggers a singularity; Futurama travel to a future of Big Rip followed by a new, almost identical Big Bang; The amazing world of Gumball It plays with the void between universes.
In video games and comics, references such as AI appear. With Durand in the saga Marathonobsessed with escaping the end; the Marvel Multiverse with the M'Kraan crystal as its axis; Magic: The Gathering It organizes its narrative into planes within a multiverse; Las Tortugas Ninja y Farscape They explore intersections between dimensions; JoJo's Bizarre Adventure (Stone Ocean) introduces a power that accelerates time to create a new universe; and the fan comic Dragon Ball Multiverse organizes tournaments between parallel universes.
Even recent audiovisual dissemination has rekindled interest. On March 20, 2019, the creator melodysheep He published “TIMELAPSE OF THE FUTURE: A Journey to the End of Time”, a 29-minute video that explores possible cosmic futuresaccumulating tens of millions of views and a huge number of "likes".
Classic models discarded and renewed possibilities
During the 20th century, some models considered a universe closed and finite which, after expanding, would contract to a catastrophic implosion (the Great Implosion). Today, most of those models have been abandoned because observations point to an expansion. accelerated which suggests a Big Freeze rather than a Big Crunch.
Even so, new interpretations of the dark matter and, above all, proposals in which dark energy is dynamic and could dilute or change sign, have brought back to the forefront the possibility of a universe oscillating or a reversion future. Hence the interest in models that place the start of the contraction several billion years from now.
A metaphor that transcends physics
Beyond science, the Big Crunch is used as metaphor of closure and rebirth. It is not uncommon to find companies or projects that, inspired by this idea, talk about to stop, contract, and be reborn with a new identity, as happens in stories of corporate “philosophies” that are presented as a “Great Collapse” of their own to kickstart a new universe of opportunities. It's a cultural nod that demonstrates the extent to which the fate of the cosmos permeates our imagination.
What would we see in a universe that slows down and collapses?
If the Big Crunch were ultimately our destination, we would initially notice that the expansion slows: dark energy loses steam, the gravity It regains control, and cosmological redshifts become less intense. After the point of maximum size, the expansion reverses and the blue shifts would gain prominence.
Over time, clusters and superclusters would regroupGalaxies would collide in cascades, average temperatures would rise, and the universe would become denser and hotterIn the final stage, the quantum physics of gravity should come into play to describe exactly what happens near the supposed singularity.
In this scenario, some authors have speculated that, after the collapse, a new Big Bang could turn on Another expansion. Others place the endpoint at a singularity that gives rise to nothing more. The difference between the two images depends on physics beyond of the current models, so it remains an open field for research.
Currently, the best measures "weighing" the universe favor the indefinite expansion and an outcome by thermal deathBut the community's interest in parameters such as ΩThe nature of dark energy and the possible vacuum transitions are enormous, because the grand finale depends on them. eternal freezera tear, a collapse, or a rebound.
