Imagine living in a bubble. Not a soap bubble, but a space-time bubble, where time flows at a different rate than in other regions of the universe. This is the basic concept of Timescape Cosmology, one of the alternative cosmological theories that are gaining increasing attention among experts.
According to this model, the apparent acceleration of the expansion of the universe that we today attribute to the mysterious dark energy It could actually be just an optical illusion, the result of “playing” with cosmic clocks that beat different rhythms. An idea that could rewrite the history of the cosmos as we know it.
The standard cosmological model under scrutiny
To understand the significance of these new theories, let's take a step back. The current reference cosmological model, known as ΛCDM (Lambda-Cold Dark Matter), describes a universe dominated by 95% of “dark” components: the dark matter, which explains the extra gravitational effects we observe on galaxies and clusters, and dark energy, a mysterious repulsive force that would cause the accelerated expansion of the cosmos.
Despite its successes, the ΛCDM model leaves many questions open about the nature of these exotic ingredients. This is where alternative theories come in.
Timescape Cosmology, “Queen” of Alternative Theories? A Universe of Time Bubbles
The timescape cosmology, the theory developed by the New Zealand physicist David Wiltshire, assumes that the universe is much less homogeneous than assumed by the standard model. Huge voids alternate with dense regions of matter, such as filaments and galaxy clusters. According to Wiltshire, these differences in density translate into differences in the rate at which time passes: Atomic clocks in a galaxy might tick up to a third slower than those in a vacuum.
This is no small feat: on cosmic scales, in fact, billions of years more would have passed in the “emptier” areas than in the “denser” areas.
Is the acceleration of the universe just an optical illusion?
The “Timescape” model would have crucial implications for how we interpret the expansion of the universe. When we look at very distant objects, their light passes through these time “bubbles”: if they are beyond a large void, they will appear to move away faster than objects at the same distance but in a denser area.
As voids occupy a larger and larger portion of the cosmos over time, it would give the illusion of a global acceleration of expansion. A purely prospective effect, without the need to invoke dark energy.
Evidence of supernovae
Yes, ok, but does this theory really “work”? To put it to the test, a team of astronomers analyzed a sample of 1535 type Ia supernovae, “standard candles” whose brightness allows us to precisely map cosmic distances and velocities. Result: the data fit the timescape cosmology slightly better than the ΛCDM model.
It's not definitive proof, of course, but it's a serious indication that something might not add up in our current description of the universe.
From alternative theories to a new era of cosmology?
Are we at a turning point? It may be too early to tell. The Standard Model remains a formidable framework, and other alternative theories (from modifications of gravity to multiverse scenarios) are equally competing to explain the mystery of cosmic acceleration. But one thing is certain: cosmology is an open and bubbling construction site of innovative ideas, where old certainties are questioned and new horizons open up.
Whether timescape cosmology or another model prevails, the next few years will see a revolution in our understanding of the universe. New missions like Euclid and the Vera Rubin will collect data of unprecedented precision to verify these theories. And who knows, maybe the same instruments that gave the Nobel Prize for dark energy will end up signing its “death certificate”. After all, this is how science proceeds: through challenges, revolutions and twists. We can't wait to find out how it will end.
