What’s wrong with the Universe?
For centuries now mankind has been pretty sure it knew what the Universe was made of – gas, dust, stars, planets, galaxies, hamburgers – those were considered to be the main constituents of the cosmos. Some of the dust and gas may have been a little hard to see, some of the galaxies were so far away that their light was incredibly faint by the time it reached the Earth, but essentially we knew what the raw ingredients were (apart from the burgers but who cared, they tasted so good).
For the last hundred years or so we have also had a good working model of the way the Universe came into existence and how it has evolved since – the famous Big Bang theory (the scientific hypothesis, not the TV show). This says that at some point in the past (around 15 billion years ago) the entire Universe came into existence at a point, exploded outwards and has been expanding ever since. This latter conjecture has been verified experimentally numerous times by measuring the so-called red shift of other galaxies as they rush away from each other. The effect is analogous to the way a train whistle or a siren appears to change in pitch as the vehicle approaches and then recedes from an observer (a phenomena known to physicists as the Doppler effect).
|Sound waves from a moving vehicle distorted by the Doppler effect (Image credit Charly Whisky)|
Of course in much the same way as a ball thrown directly upwards on Earth will slow down due to the effect of gravity as it rises higher and higher, it was understood that the rate of expansion of the Universe would slow down over time. What would happen once the rate reached zero was unclear, this depended on how much matter the entire Universe contained. Nonetheless the slowing of the expansion was taken as given.
Imagine the surprise of two separate groups of physicists therefore when studies they were carrying out to determine the distances to a class of exploding star known as Type 1a supernovae indicated that the rate of this expansion was not slowing down, in fact the total opposite, it appeared to be speeding up. This would be like throwing a ball straight up into the air only to see it speed up faster and faster and fly off into space! Both groups initially doubted their own findings and it was only when they became aware of the work of the others that they were able to accept that they had discovered a new phenomenon, rather than having made some huge experimental error.
|A supernova remnant, or possibly a giant cosmic space pizza|
(Image credit NASA)
In fact their findings are now so well accepted by mainstream science that three of the men have been awarded this years Nobel prize for physics, usually reckoned to be a good indication that you are on the right track with your work.
In order to explain this result a mysterious and so far unobserved mechanism was proposed, currently going by the name of Dark Energy – the name being chosen to indicate that we don’t really have a clue what this consists of. It is hoped that future observations by instruments such as the James Webb Space Telescope (due for launch in 2018) will shed light (literally) on the answer, until then there are a range of weird and wonderful ideas being bandied about as explanations.
|The sum total of human knowledge about exactly what comprises dark energy|
Of course this is all great news for physicists, the more cynical amongst us may well feel that ‘discovering’ something huge yet invisible is a great way to guarantee future employment and funding for massive science projects such as the JWST or the LHC, but of course physicists are far too naïve and innocent to ever cook up such a scheme – aren’t they?