Since ancient times, human beings have believed the night sky might hold the key to our existence.

And yet for hundreds of years the universeEverything. Including all of time and space and its contents. has toyed with us, yielding up some of its secrets only to perplex us with an even tougher poser.

Three years ago, a new Dark Energy Spectroscopic Instrument (DESI) was created in ArizonaA state in the southwest USA with a population of more than 7 million. to answer one of the most complex of these questions: dark energyAn unknown form of energy causing the expansion of the universe to accelerate..

Dark energy started as a scientific theory to solve the big headscratcher of 20th Century physics. By this time it was well known that the universe was expanding. 

However, traditional NewtonianRelated to the work of Sir Isaac Newton, the English physicist and mathematician who is known for his discovery of gravity. ideas would suggest that this expansion should begin to slow under the effects of gravityAn invisible force that pulls objects towards each other. Earth's gravity keeps us on the ground and makes things fall. It is less strong on Mars.. Instead, it has been accelerating.

Scientists thought this must be caused by something capable of countering gravity. They gave it the name "dark energy". Physicists calculate that fully 68% of the density of the universe is made up of it.¹

It is unlikely we can do anything useful with dark energy, as the amounts we would theoretically be able to harness would be too small.² However, understanding it is key to predicting the fate of our universe.

If the universe continues to expand, then it will eventually suffer "heat death", where all the energy in the universe slowly disappears.³

More dramatically, dark energy could ultimately tear apart all ordinary matter. This outcome is colloquiallyLanguage that is used in ordinary conversations. Informal language. known as the "big rip".⁴

But between now and 2030 we might yet discover still stranger things about dark energy. Scientists always thought that the universe expands at the same rate in all directions, meaning this energy must be the same everywhere.

However, preliminary results from DESI suggest this might not be true. Instead, it seems that dark energy might have changed over time, becoming weaker today than it was in the past.

One group of scientists has an even more radicalExtreme. theory: that dark energy does not really exist. They argue the universe is not expanding at the same rate everywhere; it is growing in a "lumpy" way.⁵ As such, there is no need for dark energy to explain anything.

In other words, everything we thought we knew for half a century could be wrong. Will 2030 prove us wronger still?

Will we be astonished by how little we know now?

Yes: So far both measurements taken by DESI and more theoretical work are overturning everything we thought we knew about dark energy in 2025. By 2030 we might need an all-new theory.

No: The DESI findings are very speculative and few scientists accept the idea that dark energy does not exist. By 2030 we will probably have confirmed everything we thought was true.

Or... The secrets of the universe are waiting to be discovered. But political, social, and climatic events here on Earth may yet prevent us from ever uncovering them.