Dark Energy May Not Exist: Something Stranger Might Explain The Universe
An artist's impression of the cosmic web (Volker Springel/Max Planck Institute for Astrophysics/et al)
There might not be a mysterious 'dark' force accelerating the expansion of the Universe after all. The truth could be much stranger – bubbles of space where time passes at drastically different rates.
The passage of time isn't as constant as our experience with it suggests. Areas of higher gravity experience a slower pace of time compared with areas where gravity is weaker, a fact that could have some pretty major implications on how we compare rates of cosmic expansion according to a recently developed model called timescape cosmology.
Discrepancies in how fast time passes in different regions of the Universe could add up to billions of years, giving some places more time to expand than others. When we look at distant objects through these time-warping bubbles, it could create the illusion that the expansion of the Universe is accelerating.
Two new studies have analyzed more than 1,500 supernovae to investigate how likely the concept could be – and found that the timescape model might be a better fit for observations than our current best model.
The standard model of cosmology does a pretty good job of explaining the Universe – provided we fudge the numbers a bit. There doesn't seem to be enough mass to account for the gravitational effects we observe, so we invented an invisible placeholder called dark matter.
There also seems to be a strange force that counteracts gravity, pushing the cosmos to expand at accelerating rates. We don't know what it is yet, so in the same spirit we dubbed it dark energy. All of this comes together, along with ordinary matter, to form what we call the lambda cold dark matter (ΛCDM) model.
Universe History
A diagram showing the history of the Universe according to the lambda cold dark matter model. (NASA)
The problem is that this model uses a simplified equation that assumes the whole Universe is smooth, and expands at the same speed everywhere. But it's far from smooth out there: we see a colossal cosmic web, criss-crossed by filaments of galaxies separated by vast voids emptier than we can comprehend.
Timescape cosmology takes that 'lumpiness' into account. More matter means stronger gravity, which means slower time – in fact, an atomic clock located in a galaxy could tick up to a third slower than the same clock in the middle of a void.
When you stretch that over the huge lifespan of the Universe, billions more years may have passed in the voids than in the matter-dense areas. A mind-boggling implication of that is that it no longer makes sense to say that the Universe has a single unified age of 13.8 billion years. Instead, different regions would have different ages.
And since so much more time has passed in the voids, more cosmological expansion has taken place there. Therefore, if you look at an object on the far side of a void, it would appear to be moving away from you much faster than something on this side of the void. Over time, these voids take up a larger proportion of the Universe, creating the illusion of an accelerating expansion, without needing to conjure up any dark energy.
In 2017, astronomers from the University of Canterbury in New Zealand tested timescape cosmology against observations, and found that it was a slightly better fit than ΛCDM to explain cosmic expansion. More data was needed.
So for the new studies, an astronomy team from the University of Canterbury and the German University of Heidelberg has collected and analyzed that extra data in the form of a catalog of 1,535 Type Ia supernovae. These explosions shine with a predictable brightness every time, so shifts in their light can reliably reveal distance, speed and direction of movement. As such, they're often called 'standard candles.'
This time, the astronomers say they've found "very strong evidence in favor of timescape over ΛCDM." This suggests a potential need to rethink the foundations of cosmology.
"Dark energy is a misidentification of variations in the kinetic energy of expansion, which is not uniform in a Universe as lumpy as the one we actually live in," says David Wiltshire, a physicist at the University of Canterbury.
"The research provides compelling evidence that may resolve some of the key questions around the quirks of our expanding cosmos. With new data, the Universe's biggest mystery could be settled by the end of the decade."
Both studies were published in the journal Monthly Notices of the Royal Astronomical Society.
The idea that dark energy may not exist and that an alternative explanation—such as timescape cosmology—might better describe the Universe's expansion is a fascinating challenge to the prevailing ΛCDM (Lambda Cold Dark Matter) model. Here’s a breakdown of the key points and implications:
1. The Nature of Time and Gravity
Time passes at different rates depending on gravitational strength. In areas with stronger gravity (more matter), time moves slower. In emptier regions of space (voids), time moves faster.
This uneven passage of time across the Universe could lead to varying rates of expansion in different regions.
2. Timescape Cosmology
This model incorporates the Universe's "lumpiness," acknowledging that matter is unevenly distributed in a cosmic web of dense filaments and vast voids.
In regions with more matter (stronger gravity), time moves slower. In voids, billions more years may have passed, allowing for greater expansion.
The result is an apparent acceleration in the Universe's expansion when observed from denser regions, potentially eliminating the need for dark energy.
3. Testing the Theory
Recent studies analyzed the light from 1,535 Type Ia supernovae (standard candles) to measure distances and speeds.
The findings show that timescape cosmology might align better with the observed data than the ΛCDM model, offering "very strong evidence" for the theory.
4. Implications for Cosmology
The ΛCDM model assumes the Universe is smooth and expands uniformly, which may oversimplify reality. Adjusting for lumpy structures and varying time rates could redefine our understanding.
If timescape cosmology is validated, it challenges the need for "dark energy" as a mysterious force driving acceleration.
5. Rethinking the Universe's Age
In timescape cosmology, the concept of a single unified age for the Universe (13.8 billion years) becomes meaningless. Different regions could have vastly different ages due to their time dilation effects.
6. Potential Resolution
The idea suggests that "dark energy" might simply be a misinterpretation of variations in the kinetic energy of expansion in a non-uniform Universe.
With more data and refined methods, cosmology could shift fundamentally by the decade's end.
7. Broader Perspective
This theory doesn’t deny the ΛCDM model's utility but offers an alternative that could resolve inconsistencies.
Future observations, such as those from the James Webb Space Telescope and upcoming surveys, could further test this theory.
The research invites deeper exploration into the fabric of spacetime, challenging existing paradigms and opening new paths to understanding the cosmos.
Recent studies have provided compelling data challenging the existence of dark energy and supporting alternative models like timescape cosmology. Here's an overview of these findings:
1. Timescape Cosmology and Supernova Observations
Researchers from the University of Canterbury analyzed a comprehensive set of Type Ia supernovae data, which serve as standard candles for measuring cosmic distances. Their analysis suggests that the observed acceleration in the universe's expansion could be an illusion caused by the uneven distribution of matter and the resulting time dilation effects. This challenges the necessity of dark energy in explaining cosmic acceleration.
2. DESI Observations and the Nature of Dark Energy
The Dark Energy Spectroscopic Instrument (DESI) has been instrumental in mapping millions of galaxies, providing high-precision data on the universe's expansion. Recent DESI findings indicate that the expansion rate may not be uniform, suggesting that dark energy might not be a constant force as previously thought. This opens the possibility that the effects attributed to dark energy could be due to other factors, such as the universe's complex structure.
3. Implications for the Standard Cosmological Model
These findings challenge the ΛCDM model, which posits dark energy as a constant force driving the universe's accelerated expansion. The observed data inconsistencies suggest that this model may oversimplify the universe's true nature, necessitating a reevaluation of our cosmological theories.
4. Future Research Directions
The scientific community is actively seeking more precise data to test these alternative models. Upcoming observations and analyses aim to determine whether the universe's expansion is influenced by factors other than dark energy, such as variations in gravitational forces across different cosmic regions.
In summary, recent data and analyses provide substantial evidence supporting alternative explanations to dark energy for the universe's accelerated expansion. These findings encourage a reexamination of existing cosmological models and underscore the need for further research to deepen our understanding of the universe's true nature.
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