Timescape: Dark energy doesn't exist, resulting in 'lumpy' universe expansion

Dark energy has long been seen as the invisible force behind our Universe’s accelerating expansion. This mysterious component was thought to make up nearly 70 percent of the cosmic energy budget.

A new study, however, raises a different idea: maybe the Universe is expanding in a “lumpy” manner, which means dark energy might not be needed to explain those puzzling measurements of distant supernovae.

Dark energy and expansion

For almost a century, scientists have assumed that the cosmos spreads out uniformly in every direction, with dark energy speeding up that expansion.

The notion was adopted after researchers saw exploding stars, known as supernovae, appearing farther away than expected.

When calculations showed that galaxies seemed to be drifting apart too quickly, dark energy became an easy placeholder for the unknown physics.

Professor David Wiltshire from the University of Canterbury in Christchurch, New Zealand has been examining this challenge in more detail.

His research team’s analysis of supernova light curves suggests the Universe may be more uneven than we assumed.

Their approach leads to a fresh explanation for the changes in light we see, one that focuses on how time passes differently in various gravitational conditions rather than appealing to an unseen substance.

Why many have relied on dark energy

Dark energy has been tied to the so-called Lambda Cold Dark Matter model, or ΛCDM model.

This model has served as the bedrock of modern cosmology for decades. Scientists had no direct means to detect or measure dark energy, so they relied on the apparent acceleration seen in distant supernovae.

They also looked to patterns in the Cosmic Microwave Background, which is often described as the faint afterglow of the Big Bang.

Over the years, more data have hinted that there could be tension between early and recent expansion rates, sparking serious questions about whether we are missing some major puzzle piece.

Enter the timescape model

The new work supports something called the timescape model, which does not need dark energy to explain cosmic acceleration. Instead, it notes that local physics can vary depending on how mass is distributed.

One clock drifting through a sparse region of the cosmos might tick faster than the same clock inside a galaxy packed with more gravitational pull.

The team’s findings were featured in the journal Monthly Notices of the Royal Astronomical Society Letters.

“Our findings show that we do not need dark energy to explain why the Universe appears to expand at an accelerating rate,” noted Professor David Wiltshire, who led the study.

He sees this approach as an opportunity to rethink the way we average cosmic expansion. “The Universe’s biggest mystery could be settled by the end of the decade,” Professor Wiltshire claimed.

Hubble tension and the lumpy Universe

Part of the growing dispute involves something called the Hubble tension.

Measurements of the early cosmos from the Cosmic Microwave Background suggest a certain rate of expansion, while observations of supernovae in the present day reveal a faster pace.

This inconsistency has triggered re-examinations of old assumptions. Adding to that, the Dark Energy Spectroscopic Instrument (DESI) has discovered that the standard ΛCDM model may not line up perfectly with some of its new high-precision data.

Researchers are looking into models where dark energy might change over time, but the timescape idea takes a different path: it challenges the uniformity assumption at its core.

Rethinking dark energy

If the Universe is lumpy, with matter clumping in some regions and emptier voids in others, then local gravitational effects might skew the calculations that gave dark energy its place in cosmic theory.

Traditional equations used to describe expansion were first introduced almost a hundred years ago, so some researchers argue that the Universe’s complex structures were overlooked.

This new study insists that a uniform expansion might not be the full story. When you allow for different gravitational influences, dark energy becomes optional.

Looking ahead to fresh data

Several upcoming projects are on the horizon.

The European Space Agency’s Euclid satellite launched in July 2023, and future missions like the Nancy Grace Roman Space Telescope promise more comprehensive observations of supernovae.

The timescape team believes that at least 1,000 high-quality supernova measurements could be enough to show if their approach really works.

If timescape ideas pass these tests, the so-called “biggest mystery” might get resolved sooner than people think.

What does all of this mean?

To sum it all up, the Universe is more intricate than any simple map might reveal. If the timescape model holds up under further scrutiny, there could be wide-ranging effects on cosmic models, especially those that rely on dark energy as a key ingredient.

Astronomers, physicists, and cosmologists will be watching closely as more data come in from cutting-edge surveys and instruments.

These results might bring clarity to the Hubble tension or uncover new clues about the structure and history of everything around us.

Dark energy has been the leading explanation for cosmic acceleration for decades. Yet, if local gravitational differences and variable clock speeds can account for what we see, the door may be open to a more nuanced story of cosmic growth.

There is no shortage of skepticism within the scientific community, but unexpected solutions to old puzzles are often how we expand our understanding of the Universe.

If the timescape approach stands the test of fresh observations, future textbooks might look a little different.

The full study is published in the Monthly Notices of the Royal Astronomical Society: Letters.

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