Universe is expanding too fast, say scientists

Space out: Snapshots of the universe taken by the Hubble telescope’s “ultra deep field”. © NASA

Scientists have found a troubling statistic in their observations of the universe: it is expanding about 9% faster than it should. Why is this happening? And should we be worried about it?

This story starts (as all stories do) with the Big Bang. Around 13.7 billion years ago, the universe exploded into being. It has been expanding ever since. But how quickly?

The answer depends on the distance between things. Imagine it like a blueberry muffin rising in the oven. As the cake expands, the berries move further away from each other. But the berries in the middle are moving apart more slowly than those at the edge.

The same principle applies to the speed at which galaxies are drifting apart in space.

Measuring this speed involves a number called the “Hubble constant”. If you look at radiation leftover from when the universe was just 380,000 years old (what some call a “cosmic baby picture”), then the number is 67. Or rather — for every 3.3 million light years further away something is, it is travelling 67km per second faster.

However, scientists measuring the distance between bright objects like quasars and supernovae put the Hubble constant at around 72.

In other words: the universe is expanding 9% faster than it should be. This is a problem — and scientists cannot agree on why it is happening. Three of the main theories include:

1/ Previously undiscovered particles were present at the start of the universe, thrusting it forward more quickly.

2/ A mysterious field or force, known as “early dark energy”, appeared when the universe was around 100,000 years old, sped everything up, then blinked off again another 100,000 years later.

3/ Dark energy, which physicists believe is somehow related to the expansion of the universe, is getting stronger.

“We are confused,” the cosmologist Michael Turner told The New York Times, “and hoping that the confusion will lead to something good!”

The answer to this question matters. If theory number three is correct, and dark energy is getting stronger all the time, it could be bad news for humanity. Too strong, and it could overtake gravity itself, causing Earth and all its atoms to suddenly tear apart.

Then again, there are other possible explanations. “Maybe the universe does this from time-to-time?” suggested Nobel Prize-winning physicist Adam G. Riess.

Or perhaps scientists have simply made a mistake.

Reach for the stars

How should all this make us feel? Is it alarming to think that some of the best scientists of our time are so perplexed by this question? After all, the future of the universe itself is at stake. What good is science if it does not give us the answers?

Or should we be comforted by the knowledge that there are still things left to discover? This is a known unknown — we may not have the answer yet, but we know to start looking. Far scarier are the things that we don’t know we don’t know.

You Decide

  1. Is it worrying to think that scientists do not know why the universe is behaving this way?
  2. Will we ever know everything about how the universe works?


  1. Write a list of other questions that you have about the universe and how it works. Choose one, and see if you can find out the answer using your own research.
  2. Look at the images of the universe at the top of this story, featuring galaxies of many ages, shapes and colours. Write a short story about one of them.

Some People Say...

“The universe is under no obligation to make sense to you.”

Neil deGrasse Tyson

What do you think?

Q & A

What do we know?
The universe is both expanding and accelerating. Scientists measure the speed at which an object (such as a galaxy) is moving away from us by how much its light wavelengths have shifted, a process known as red shift. Distance is measured by comparing the brightness of “standard candles”, such as stars or supernovae. With these measurements you can begin to piece together the rate at which the universe is expanding.
What do we not know?
Why that rate seems to be faster now than scientists think it should be. There could be any number of explanations, but they are difficult to prove unless a new particle (or something similar) is discovered. After all, scientists do not even know what dark energy is, let alone whether it is getting stronger. It is all just theory.

Word Watch

Big Bang
The generally accepted scientific theory of the beginning of the universe.
Named after Edwin Hubble, an American astronomer who not only discovered the existence of galaxies beyond our own, but also the fact that they were moving away from us as the universe expanded.
Known as the “cosmic background radiation”, or CBR. It is leftover from the very early stages of the universe, and so offers a glimpse back to the beginning of time.
3.3 million light years
Also known as one megaparsec.
The brightest objects in the universe, powered by supermassive black holes. They can be 10 or even 100,000 times brighter than the Milky Way.
The largest explosions in space, which take place when a large enough star reaches the end of its life.
Dark energy
A mysterious entity which makes up about 68% of the universe — however, we cannot see it, and therefore cannot study it. Although no one is sure what it is or how it works, it seems to be related to the expansion and acceleration of the universe.



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