Like the Big Rip, but with no fixed end date. The tearing-apart takes forever to complete.
The Little Rip
Dark energy still grows without bound and still tears structures apart, but its density diverges only as time runs to infinity, so there is no finite-time doomsday.
Looping ambient scene for Rip Scenarios. The rip futures all follow from phantom dark energy: a dark energy whose density increases as the universe expands, which happens when its equation of state w sits below -1. A growing repulsion does not just accelerate the expansion, it strengthens without limit, so structures held together by gravity, then by electromagnetism, then by the nuclear forces, are progressively unbound. The variants differ in how the energy density grows and therefore in whether the end comes at a finite time (the Big Rip), only as time runs to infinity (the Little Rip), or in an intermediate way that spares some structures (the Pseudo-Rip and the Little Sibling of the Big Rip). All of them rest on the premise that w is below -1, which current data neither confirm nor exclude.
§1 · The claim, in one sentence
The Little Rip is a softer cousin of the Big Rip. The phantom-like dark energy density still increases without limit and still eventually unbinds galaxies, stars, and atoms, but it diverges only as time goes to infinity rather than at a finite moment. Frampton, Ludwick, and Scherrer 2011 introduced it to show that a dark energy can dismantle every bound structure without producing the finite-time singularity that makes the Big Rip mathematically awkward.
§2 · Why it might be true
The Big Rip's most troubling feature is its finite-time singularity: the scale factor reaches infinity at a specific future moment, which is a genuine breakdown of the equations. Frampton, Ludwick, and Scherrer 2011 asked whether you can keep the destructive growth of phantom dark energy while avoiding that singularity.
Their answer is the Little Rip. Here the dark energy density rises steadily but the equation of state w approaches -1 from below just slowly enough that the scale factor diverges only at infinite time. There is no doomsday date on the calendar. Yet the inertial force pulling on any bound system still grows without bound, so given enough time it exceeds the binding force of clusters, then galaxies, then the Solar System, then atoms.
The Little Rip therefore ends the same way as the Big Rip, with everything unbound, but it never hits a moment where physics stops. This makes it more palatable to many theorists while keeping a sharp observational signature: a dark energy whose w sits below -1 today and curves back toward -1 over time, rather than holding at a constant phantom value.
The family stance
The universe ends by being torn apart. A dark energy that grows stronger over time eventually overwhelms gravity and every other force, dismantling bound structures from the largest scales down to atoms. Whether this happens at a finite future moment or only asymptotically depends on exactly how the dark energy density grows.
§2.5 · Evidence
- The Little Rip removes the finite-time singularity that makes the Big Rip theoretically uncomfortable, so it is the more defensible way to realise a tearing-apart future
- It remains a phantom-type model with w below -1, a region current data leave marginally open
- It makes a specific, testable prediction about the time evolution of w, distinct from both a cosmological constant and a constant-w Big Rip
§3 · What you'd need to test it
- Dark energy density increases without bound but the scale factor diverges only as time runs to infinity, so there is no finite-time singularity
- All bound structures are still eventually unbound, in the same order as the Big Rip, but on an open-ended timeline
- The equation of state w sits below -1 and asymptotes back toward -1, a distinctive evolution that surveys mapping w(z) could detect
- Distinguishing the Little Rip from the Big Rip requires measuring not just w but how w changes with time
§4 · Where it breaks
- Like every rip future it needs w below -1, for which there is no positive evidence
- It still relies on phantom dark energy with the associated ghost-instability concerns, merely deferring rather than removing the deep theoretical problem
- Its observational signature is subtle and only diverges from the Big Rip and from heat death in the far future, so present data cannot cleanly select it
Go deeper
Frampton, Ludwick, and Scherrer 2011 (Phys. Rev. D 84, 063003) construct dark energy models where the density rho grows but the integral that determines the scale factor diverges only at infinite time. The key quantity is the inertial force on a bound system, which depends on the Hubble rate and its time derivative. In the Little Rip this force grows without bound even though the universe never reaches infinite size in finite time, so dissolution is guaranteed but never instantaneous.
The Pseudo-Rip, introduced by the same authors a year later, is the limiting case where the Hubble rate rises toward a finite constant rather than infinity. There the inertial force approaches a ceiling, so some loosely bound systems are torn apart while more tightly bound ones survive. The Little Rip, Pseudo-Rip, and Big Rip thus form a sequence parameterised by how fast the dark energy density grows.
Cross-references: the Big Rip variant in this family is the finite-time limit, and the Pseudo-Rip is the gentler limit where structures can survive. All three connect to the Phantom Energy variant in the Chapter 5 Dark Energy Candidates family, which is where the w-below-minus-one premise is treated as a dark-energy-identity question.
Variants in this family
Compare variants▸§5 · Who built it, and when(1 source, 1 established)
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