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The Science Behind Dark Energy

Irina Slav

Major scientific breakthroughs happen precisely because of this singular psychological manifestation: scientists get excited about what they don’t know.

Now, long the butt of jokes by laymen who don’t know the first thing about astrophysics, scientists may just have the last laugh. 

A “super telescope” is about to reveal the secrets of time and space. 

And if you didn’t realize you were obsessed with time and space, think again. We are a race consumed with time and space, as enshrined in our long-standing passion for time travel, which has only been possible in science-fiction books and films. 

We think of time in terms of space, and we’ve never been able to explain it. 

Thanks to that laughable instinct of the astrophysicist, though, we just might get a life-changing explanation. 

Meet DESI, the Dark Energy Spectroscopic Instrument. Last month, DESI was mounted on the Myall telescope in Arizona and it has already captured its first images of the universe. 

DESI is the result of collaboration among 500 researchers from 13 countries. A super-telescope made up of 5,000 separate mini-telescopes, each capable of taking a snapshot of a different galaxy every 20 minutes.

The purpose of the project is to map the distance to 35 million galaxies and 2.4 million quasars to see how the universe has expanded and how it continues to expand. Ultimately, its goal is to determine whether dark energy could turn out to be gravity’s counterforce and all the potential implications of that massive discovery.

A little background first before things get really complicated... 

The material universe, according to scientists, constitutes a measly 5 percent of the total universe. That’s 5 percent of what NASA calls “normal matter”, such as planets, stars, and similar formation. Another 27 percent of the universe is constituted by the sinister-sounding dark matter. About this dark matter, NASA has this to say: “We are much more certain what dark matter is not than we are what it is.”

The remaining 68 percent of the universe, according to this dominant hypothesis, is constituted by dark energy.

Nobody has seen this dark energy. And like dark matter, nobody is really certain what it is. But there seems to be reason to believe that it could be the counterforce of gravity.

How did this hypothesis come about? That’s a really interesting story.

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For a very long time, scientists believed the universe had been expanding up to a point before it began contracting, pulled back by gravity. Imagine their surprise in 1998 when a team of astronomers discovered that the universe was still expanding-and, adding insult to injury, it was expanding faster than before. 

Naturally, the people who discovered this received the Nobel Prize, but that was just the start of the hard work. It opened up a Pandora’s Box of new questions: How, why and what is causing this expansion?

The ‘why’ remains elusive. But the ‘what’ has been answered, hypothetically: dark energy.

Even though scientists have yet to establish what exactly dark energy is, many of them seem to agree that it is the driving force of the universe’s continued expansion, counteracting the universal pull of gravity.

As to the ‘how’, there are several possibilities, all stemming from the existence of dark energy. One focuses on something called “vacuum pressure”, according to the BBC, which is the result of fluctuations in the time-space continuum on a sub-atomic level. Calculations of this vacuum pressure turned out to be a much higher number than expected: 10 to the 120th power, which is 10 with 120 zeroes after it. This is a lot stronger than the force astronomers have observed in the universe as driving galaxies apart. This led some to assume a mistake was made in the calculations. Others began speculating.

One theory suggests we live not in a universe; but rather, in a multiverse - and while our universe has a relatively weak vacuum pressure, others have much stronger vacuum pressures, and these are pulling our universe into expansion.

Another theory considers dark energy as a property of space. Space, as Einstein told the world, is not empty. It has its own properties. If dark energy is one such property, then as space expands, so does its energy.

Yet another theory comes from quantum physics and involves the concept called “vacuum pressure” above. Instead of pressure, quantum scientists explain the energy with the presence of virtual, temporary particles in empty space. These particles form and disappear, and in the meantime, apparently, produce energy. It was in calculating this energy that the 10 with the 120 zeroes after it surfaced, confusing a lot of people.

One other theory stipulates that dark energy is some sort of fluid or field that fills space and counteracts gravity Nobody knows what properties it has and how it interacts with other components of space-time.

And then there is the possibility that Einstein’s theory on gravity was either inaccurate or incomplete. This, if somehow proven, could turn physics maybe not on its head but certainly sideways, as science rethinks a lot of the concepts and processes that had previously taken as fact.

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So how does one go about finding a proof for any of these theories? By aggregating data, of course, and then analyzing it. This is exactly what DESI would be doing. It will be generating images of galaxies both far, far away and ones nearby, and others in the middle, to tell scientists how the universe is expanding. The fundamental simplicity of the whole process is beautiful: as the BBC’s Pallah Ghosh puts it, “The further DESI looks into space, the further back in time it sees.”

As it does so, it will generate a lot of data about the expansion of the universe, spatial and historical, and this data will be much more accurate than previous attempts at mapping the universe. With any luck, the data will produce answers about the nature of dark energy and, consequently, the nature of our universe.

Unsurprisingly, not everyone is so enthusiastic. 

Four years ago, a physicist from Oxford University challenged the findings of the Nobelists who said the universe was still expanding, and rapidly, at that. Subir Sarkar and two other physicists argued that the evidence was insufficient for such a conclusion, based on a statistical analysis of the first team’s data.

Once again, unsurprisingly, this challenging study also became the target of criticism, which accused researchers of cherry-picking the data for their statistical analysis in order to fit their hypothesis.

In what may be turning into a genuine scientific feud, Sarkar and his colleagues have just published a second paper, which this time challenges the very idea that the universe is still expanding. According to that paper, what the Nobelists thought was a universal expansion was just a local expansion in our corner of the universe.

It is at times like this one can really appreciate how far technology has come. 

While scientists argue in papers, DESI will be taking pictures of galaxies—35 million of them—plus 2.4 million quasars. Whatever these pictures reveal, it would be hard to argue against the significance of such a body of evidence.

By Irina Slav for Oilprice.com

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