The Big Bang Theory says that the universe expanded from a once tiny starting point and the Big Crunch Theory predicts that the Universe will end up the same way; with everything crashing together again under its own gravity. This theory now appears to be wrong as a mysterious force known as Dark Energy is actually making the Universe expand quicker.

We’ve already covered the Big Bang Theory here at Matilda’s Lab but now we’re going to do something that we’ve not done before and focus a lesson on an outdated and discredited theory. “Why bother doing that?” you may wonder. Well, in order to reject an idea in science, you need to do so from a position of knowledge rather than ignorance. This means that there are still things to be learnt from looking into why this theory met its demise.

What is the Big Crunch Theory?

So let’s set the scene: The Big Bang Theory tells us that the universe and everything in it started off in a ridiculously compact form known as a singularity. This singularity expanded so the universe got bigger and it continues to expand today. The Big Crunch Theory says that the gravity of all the things in the Universe pulling on each other will eventually overcome this spread. What goes up must come down; so one day everything in the Universe will all come crashing back together again in a great big crunch. This theory appears to be completely wrong.

What’s wrong with the Theory?

When we last covered what a theory is, we said that they allow us to make predictions using explanations that are based on all of the known facts. The reason why the Big Crunch is no longer a valid theory is because it no longer accounts for all of the known facts and it does not appear to make accurate predictions.

Whilst gravity is a known fact, in order for the Big Crunch to be a possible we should see the expansion of the universe gradually slowing to the point where it stops and a collapse begins. As you may have picked up from my tone; this is simply not happening. What we know is that the expansion of the Universe is actually accelerating!

How do we know how fast the universe is expanding?

How on Earth can we know that? Put simply, we can see it happening. Whilst light travels very fast, the Universe is very big so it can still take light a long time to get somewhere. When we look at stars in the sky we are actually seeing light that was made tens, hundreds or even thousands of years ago. Some of the best telescopes that we have can see stars whose light was produced billions of years ago. Most of this light is coming from galaxies (groups of hundreds of billions of stars) rather than individual stars as the stars are too far away to been seen on their own. Because it’s taken so long for the light to reach us this makes it like a postcard sent from a holiday which arrives at its destination weeks later and therefore contains information that is no longer up to date. In the same way, this starlight is a glimpse into the past and it is these glimpses which tell us that the universe is speeding up.

A while ago we looked at the Doppler effect  and explained why noises sound different depending on whether something is headed toward you or going away from you and a similar thing happens with light. We don’t notice it on Earth as everything is too close and light travels too quickly, but over the great distances of the universe it can be seen. The sign of this happening is referred to as a red shift and it tells us that something is moving away from us.

What we see is that we are getting more of a red shift from galaxies that are closer to us than we do from the ones which are really far away. Since the closer galaxies give us more up to date information then it appears that things must be moving apart quicker than they used to.

Why is the universe not slowing down?

This begs an important question: If gravity indeed does draw things together, then why isn’t the Universe playing ball? Nobody knows for sure, but the increase in pace is being attributed to dark energy. What is dark energy? Again, nobody knows; it’s called ‘Dark’ energy because we can’t see it, we don’t know where it comes from and we can’t directly measure it. The only reason we know that it is there is because the universe appears to be expanding quicker. As a result, it is thought that it is merely a property of ’empty’ space, and the more space is produced, the more energy there is.

So is it really all over for the Big Crunch Theory?

The only hope left for the Big Crunch theory is that dark energy turns out to be a temporary effect (which could be possible as we don’t really know what it is).

So one final thought: If the Universe is not going to end up crunching together, what does the long term future look like. Well, the leading theory at the moment is the Big Freeze Theory which says that the universe will just keep on expanding until all of the stars go out and all matter eventually crumbles away until there is no matter left. Another option is the big rip; where the speed of expansion gets so fast that universe literally tears itself apart… and on that bombshell; HAVE A GREAT DAY EVERYONE!

Matilda’s Lab ©2016 Updated in 2020. https://twitter.com/matildaslab.

Matilda’s Lab is written to explain complex science to children. Effort is made to keep the content accurate but sometimes it is necessary to oversimplify things. However, if anything is factually wrong then please get in touch so that a correction can be made.