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For years scientists have thought that a strange force called dark energy is causing the universe to expand faster and faster. This is one of the puzzles in modern astronomy. It is believed to make up 68% of everything in the universe. Still no one really knows what dark energy actually is.
Now NASAs Nancy Grace Roman Space Telescope is getting ready to look into this puzzle in a detailed way. With its imaging tools and ability to see big parts of the sky Roman might find clues that make scientists rethink some of their basic ideas about space.
There is a big difference between a possible scientific idea and a confirmed discovery. Roman has not yet shown an image that proves dark energy is gone or that the rules of physics have changed. The real story is about what this amazing telescope might find when it starts its science work.
The Mystery That Has Bugged Astronomy for Years
In the 1090s astronomers looking at faraway exploding stars found something they did not expect. The universe was not slowing down because of the pull of matter. Instead it was speeding up.
This discovery changed how people understand the universe.
Scientists came up with the idea of energy to explain the speeding up. Unlike matter which pulls other matter together with gravity dark energy seems to affect the growth of space itself.
The simplest idea is that dark energy acts like a constant, a concept first linked to Albert Einstein. In this idea the strength of energy stays the same as the universe grows.
Researchers have never been sure that this is the full story.
What if dark energy changes over time? What if gravity works differently across distances in space? What if the speeding up's proof of a bigger physical idea that current theories don’t explain?
These are exactly the questions Roman is built to explore.
A Telescope Designed to Look at the Universe in a New Way
The Nancy Grace Roman Space Telescope is not another telescope taking pretty photos of faraway galaxies.
It is made to map the universe on a scale.
Its Wide Field Instrument will take pictures of parts of the sky much bigger than what the Hubble Space Telescope captures in one shot while still keeping the images clear.
This is important because understanding energy needs astronomers to look at lots of galaxies and see how the universe has changed over billions of years.
Roman will study where galaxies are measure how away they are and check for the tiny effects of gravitational lensing, where the gravity of matter bends light as it moves through space.
These observations could help scientists piece together the history of the universes expansion.
Of looking at just a few distant objects researchers will be able to see large patterns all across the universe.
Inside those patterns might be signs that the usual model of the universe is not complete.
What If Dark Energy Is Not the Same All the Time?
One of the interesting ideas is that dark energy might not act the same throughout the universes history.
If its effect has changed over billions of years the effects would be huge.
The usual model of the universe called Lambda-CDM assumes that dark energy acts like a constant. This model has worked well for observations, including the way the universe is structured and measurements of the leftover heat from the Big Bang.
Scientists keep checking if the model fits all parts of the universes history.
Some recent observations from space surveys have made people wonder if dark energy might change over time. These hints are not certain yet. They have made people more interested in future observations.
Roman could offer an separate way to test these ideas.
If its results show proof that dark energy changes over time physicists might need a better way to explain how the universe is expanding.
That would not necessarily mean dark energy doesn’t exist.
It could mean that scientists have not fully understood what dark energy really is.
The Clues About the Universe Hidden in Distant Galaxies
Imagine looking at millions of galaxies spread out over a part of the universe.
At first the picture might look like a collection of stars and galaxies.. For astronomers the most important part is not what the objects look like.
It is where they are, how away they are and how their light has been changed on its way to Earth.
Galaxies form groups, lines and walls with huge empty spaces in between. These structures grew over billions of years because of gravity and the universes expansion.
By looking at where they're at different distances scientists can find out how fast the universe grew in different times.
Roman will also use gravitational lensing to measure small changes, in the shapes of galaxies. These changes help show where matter is, the invisible dark matter.
Putting these measurements together will let scientists check how cosmic structures grew and how the universe expanded.
If the results do not match what is expected researchers will have to find out why.
The answer could be changing energy, new physics or problems with how scientists understand the measurements.
I have always been fascinated by how Einsteins general theory of relativity has stood the test of over a hundred years of experiments.
I see Einsteins theory of relativity as the key to explaining how planets move how light bends around massive objects and how gravitational waves ripple through space.
I still wonder whether Einsteins general theory of relativity describes gravity perfectly across the largest distances that exist in the universe.
Some alternative theories suggest that cosmic acceleration might not need an energy component at all.
Instead gravity itself could behave differently on large scales.
I believe Romans observations could help distinguish between these possibilities.
By comparing the expansion history of the universe with the growth of structures astronomers can test whether gravity behaves as Einsteins general theory of relativity predicts.
A convincing discrepancy would be scientifically extraordinary.
Such a result could suggest that the current understanding of gravity needs modification potentially opening the door to a new chapter of theoretical physics.
However extraordinary claims require independent measurements and careful analysis.
A single surprising image would not be enough to establish such a discovery.
Why Roman Could Change Everything
I think the greatest strength of Roman is not that Roman is guaranteed to overthrow existing physics.
The greatest strength of Roman is that the telescope will make some of the precise and comprehensive tests of cosmology ever attempted.
Scientists may discover that dark energy behaves as the standard model predicts.
Such a result would strengthen one of the successful explanations of the universe.
Alternatively they may uncover persistent deviations that point toward new physical laws.
Either outcome would be important.
Romans observations will also contribute to the study of exoplanets, distant galaxies, cosmic structure and other astronomical phenomena.
Its scientific legacy may extend beyond the dark energy question.
A New Era in Understanding the Universe
I think humanity has spent centuries trying to understand what the universe is made of and how it works.
We have discovered that galaxies are moving apart that space itself is expanding and that much of the cosmos consists of components we cannot directly see.
The most fundamental questions remain unanswered.
Why is the expansion of the universe accelerating?
What is energy?
Is Einsteins theory the description of gravity or merely part of a much larger picture?
The Nancy Grace Roman Space Telescope represents one of the ambitious efforts to answer these questions.
Its future images and measurements could confirm the cosmological model reveal unexpected behavior in dark energy or uncover evidence that forces scientists to rethink how the universe works.
Dark energy has not been declared over.
The search, for its true nature is entering an exciting new era.
If Roman finds that the universe behaves differently
from what our best theories predict the discovery could transform our
understanding of reality itself.
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