Big Bang?

What is the Big Bang? How do we know it happened? how did it get its name? What is the evidence? What does it mean if this theory is actually correct? What does it mean if the theory is wrong? what happened if the Big bang didn’t happen?

Let’s get one thing straight here. The Big Bang theory is just that, a theory. Before the 1960s the theory did not have many followers and was not really considered a serious theory to describe the universe. Yet at the current time, it is very easy to believe, especially the way that it is written about these days, that the Big Bang theory is not actually a theory but fact.

The Big Bang is not a fact. We do not know for certain that it is true. There is evidence which we will talk about below that suggests it may be true, but it is still just a theory.

In the 18th century the idea that the Earth may be millions or even billions of years old started to emerge. Most people believed well into the first half of the 20th century that the Universe was eternal and had always been here.

It was only 80 years go, within living memory, that the idea that everything may have come from a single point was first suggested by a a guy called Lemaitre ( a Belgian physicist and Roman Catholic priest no less) in 1931.

In 1912, 19 years earlier Vesto Slipher had started measuring the Doppler Shift of spiral galaxies. The Doppler shift was discovered by an Austrian physicist called Christian Doppler back in 1842. The Doppler effect explains why a police siren sounds slightly different to you if the police car is coming towards you or moving away from you. It gets slightly higher in pitch coming towards you and slightly lower when it is moving away from you. The next time you are in a street and a police car or ambulance passes you by, have a listen.

The Doppler effect can also affect light. Now, here is something really clever. Stars are made different elements much like us (in fact we were made in stars). If we take a prism and shine star light through it then we get a spectrum of light. If you do it from the light coming from the sun we get a beautiful rainbow. In fact a rainbow is just the result of rain acting like a giant prism, (more on this elsewhere).

Newton had prism made way back when so they have been around for a while. If you take a really close look at the rainbow from a prism, really close, you notice that there are actually a few gaps in the rainbow. To get a close look you can scan the rainbow by shining it into the end of a microscope. If you do this you see gaps. The are called absorption lines (this is described in detail elsewhere).

These absorption lines appear at fixed frequencies for certain elements. In our own sun we have two lines in the orange part of the visible light, we have used this to deduce that the sun is actually surrounded by Sodium gas, the same sodium gas that gives use orange street lights! Amazing eh?

So what have absorption lines got to do with an expanding universe? well, the frequency of the absorption lines changes because of the Doppler shift, just like the police siren. Slipher realised this as he looked through his telescope. He figured that this meant that the galaxies must be moving either towards us or away from us.

The universe not so long after it all started

So Slipher looks around the sky and everywhere he looks it appears that the galaxies are all moving away from us. So, hold on, does that mean that we are at the center of the universe? Not quite. Image a loaf of bread full of raisins, now as the bread is baked and starts to rise the currents get further and further apart. So it would not matter what current you were standing on all the others would seem to be getting further away from you. Even if you were right out on the edge.

Hubble, an American Astronomer confirmed the existence of galaxies other than our own in the 1920s and used Slipher’s data to develop the idea that the degree of red shift observed from other galaxies increased the further they were from the earth. This became Hubble’s law. Hubble actually doubted the interpretation of the data which lead to the development of a theory called the Metric expansion of space, which we’ll cover another day.

The idea that the universe might be expanding lead some people to the following conclusion... if it is expanding then what is it expanding from? and if we could run the clock backwards so that it was contracting, what would it contract to? Could it actually go all the way back to a single point in space and time? Enter Lemaitre the priest.

I still find it odd that it was a Catholic priest who first proposed the idea that is now considered by many atheist Physicists as the most like reason the universe came to be! Though it wasn’t always the case.

When this idea first came to light in the Physics community it was not really taken seriously. It is said that the name, Big Bang, was invented by Fred Hoyle who did not believe the idea at all and said the name as a joke. The name stuck and so did the theory! Buy why? after all if the big thinkers of the time had no faith in it, why did it become so popular that is has become the prevalent theory of cosmology at this time? Also, what did they think if they thought the Big Bang was rubbish?

Up until the 1960s the favoured theory was that the universe had always existed. In the 1940s theories on the “steady state” universe has it was known, were still being developed. The apparent expansion of the universe seen by Slipher were explained has “local” expansion. Local in this sense being the universe that we can see, implying of course that there might be and even bigger universe that we simply can’t see. Is this likely? Possibly, how would we know? there is no way we can.

So why did Big Bang win through? and why has the Big Bang risen to prominence in recent times? In the 1960s “evidence” started to emerge that strengthened the idea that Big Bang may be right. The most famous being the Cosmic background radiation, known in the trade as the CBR. It is thought that this radiation, discovered by accident in 1965 by two blokes working for Bell Labs over in the USA is left over from the earliest stages in the development of the universe. The discovery was a landmark test of the Big Bang model since this was predicted by the theory.

In the very young universe long before stars and planets formed the universe was a lot smaller, a lot hotter and filled with a lot of hydrogen and thermal radiation. As the universe continued to expand and cool, atoms started to form and it is believed that at this point they could no longer absorb the thermal radiation. This radiation has been travelling round the universe ever since! Bouncing back and forth. Though I do have a bit of a problem with this. If the universe is mostly free space, which it is, then wouldn’t most of the radiation be heading outwards, just like the galaxies, only faster? I haven’t been able to find a decent answer to this yet.

So if the Big Bang did happen how old is the universe? using the Big Bang as the starting point? well, at the current time the universe is thought to be about 13.75 billion years old (when my dad was a kid it was 3 billion). How do we know this? how is it measured? well at the moment it can be calculated using the Friedmann equation. This was developed back in 1922 by Alex Friedmann when he was working on a model of the universe in terms of General Relativity, mind blowing stuff and excruciatingly difficult mathematics. It was developed before the idea of an expanding universe was accepted and yet it is still used today, strange eg?

The up shot is that provided it is possible to measure something called the Hubble parameter, the value can be plugged into Friedmann’s equation to give us the age of the universe. In the last 10 years or so a number of experiments have been performed to give accurate values of the Hubble parameter and so, we believe, an accurate age of the universe.

But what if the Friedmann equation is wrong? would this mean that the age of the universe is wrong? well... Yes!

Are there any other experiments that we can do? The answer is that there are other methods for trying to determine the age of the universe based on the properties of stars and these set the age of the universe around about 12-18 Billion years old.

Is the Big Bang correct? Who knows? It definitely has a few things going for it, but ultimately it is just a theory and if it is correct then it raises as many questions as it answers.

If the Big Bang theory is correct then what existed before the big bang? Some will argue that it does not make sense to ask this question, but why not? To argue that time didn’t exist, that there was just the singularity I find difficult to comprehend.

Why did it happen? What does the edge of the universe look like? if the universe is expanding, what is it expanding into? What is outside the universe? Does it make sense to even ask that question?

What if the Big Bang didn’t happen?

If Big Bang theory is wrong then what alternatives are there? Would it mean that the universe really could have been around forever and that it is infinite? But this has its own problems, can the universe really have been here forever? a trillion, trillion, trillion years? How could it keep renewing the particles required for the stars? If the universe is expanding and has been expanding forever why aren't all the galaxies even further apart than they are already? Who knows?

The Big Bang is the current favourite theory of cosmology. 20 years from now it may be on the wane and a new theory may be in the ascendancy. Many theories come and go with each generation of Physicists and this may be no different. 

What do I think? I quite like the idea of the Big Bang in a way. I can actually almost imagine a universe like a 4 dimensional Mobius strip that really does have no outside.

I like the idea that the universe may have had a start, but this is just because I genuinely cannot imagine how something could have existed forever. The problem I have though is that I cannot imagine what was before the big bang, was there really nothing? 

Has this nothingness lasted forever minus the 13.75 billion years the universe may have existed?

One final thought, if the universe has been around forever then isn’t it likely that an intelligent life form other than our own must have evolved somewhere? If this happened 10s of billions of years ago isn’t it possible that these life forms would have become so advanced intellectually that they would have learned how to control and manipulate space and time? And if they still exist today why aren’t we aware of them? or are they here and are what some think of as God?

Maybe it was they who initiated the Big Bang?