Reading the online versions of the newspapers this morning over a rather soggy and unappetising bowl of Weetabix, I couldn’t help feeling a bit depressed. The economy continues to nose dive, house prices are spiralling out of control and my long suffering team Ipswich Town appear to be in the football equivalent of purgatory; not really rubbish per se, but not that great either. It was something of a delight then to read of recent discoveries in the field of Dark Energy; the mysterious force which makes up about 70 percent of the universe and is causing it's continuing expansion. It was thought that eventually (in around 50 billion years) this force will cause the universe to be torn apart in the so called ‘big rip’. Now it appears that dark energy is a constant throughout the Universe. That is, Dark Energy is not growing in strength with time, and the Universe won’t rip itself to shreds in the dim future. The article goes on to say:
"This result could be described as 'arrested development of the universe,'" said lead researcher Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in the northeastern state of Massachusetts…Whatever is forcing the expansion of the universe to speed up is also forcing its development to slow down."…After years of research, scientists now believe that dark energy is "a form of repulsive gravity that dominates the universe, although they have no clear picture of what it actually is," the research report said…What this means for the future of this universe is that accelerated expansion will proceed forever but will probably not result in a Big Rip," said Vikhlinin…."That is, nearby galaxies will eventually disappear from our sight, but the structures already formed by clusters of galaxies and our own galaxy will not be torn apart, not in the near future anyway."
Hooray!. Of course humanity is never really comfortable without the idea of an impending apocalypse, be it 40 years from now due to nuclear holocaust or billions of years from now with the heat death of the universe and I’m sure that, despite this reprieve, we will soon find some other source of ‘death from above’ to worry about.
Vikhlinin has also used NASA's Earth-orbiting Chandra X-ray Observatory to find that dark energy acts as a force that keeps clusters of galaxies — around 1,000 bright galaxies or more — from essentially overeating. Without dark energy, these giant clusters would keep forming, getting denser and bigger because of gravity. Phil Plait at Bad Astonomy puts it like this:
‘When the Universe was young, matter started to coalesce by gravity, forming huge structures millions of light years across. These collapsed to form galaxies and clusters of galaxies, like cities composed of thousands of smaller towns. …If the Universe were not expanding, forming clusters would be easy. As time went on, more matter could fall in to the cluster, forming more galaxies and making the cluster bigger. But since the Universe was expanding, there was a limit to how big the clusters could get; the outermost fringes would be moving away from the central regions, and that limited the amount of raw material available to make galaxies. It’s like going to the grocery store and trying to fill your cart with cans of spaghetti sauce, only to find workers removing the cans from the shelf at the same time. The number of cans you wind up with depends on how quickly the grocery store clerks are unshelving them.'
This leads to an interesting question, what would happen if Dark Energy were different and the galactic clusters got too big?. Well according to ‘Rare Earth by Peter Ward and Donald Brownlee, our star happens to be located in a region where star density is quite low compared to other regions of the Milky Way. In the more dense regions of our galaxy the development of life would be inhibited by supernovae and other celestial catastrophes. Too much heat and too many gamma rays or other type of ionizing radiation would disrupt the fragile development of life and all these factors would be more prevalent in a denser galactic structure. Obviously we are making assumptions based on a sample of one, but it is probable that Dark energy’s limiting of the galactic density is critical to the development of life.
In other news, a super massive black hole has been confirmed to be at the centre of our galaxy. A recent article in the Guardian claimed that this confirms that this ‘confirms we're nothing special – and that's a central tenet of modern science’.
‘The Copernican principle says that we are not the centre and focus and purpose of creation: we are a neither here nor there accretion of recycled stardust assembled by chance and the still somewhat mysterious forces that manage the universe.’
Well, there are three important points here:
1) This is a pretty sensible application of the Copernican principle. If we look out onto the universe and we see that most other galaxies have a supermassive black hole at their centre, then things should be the same for our galaxy. Sure enough that is exactly what we observe. Our galaxy is the same as any other.
2) It is becoming clear that supermassive black holes have an indispensable role in creating and sustaining galaxies. A life bearing universe needs to have a substantial amount of black holes to organise matter into galaxies. If we did not have a supermassive black hole at the centre of our galaxy, we would probably not have come into existence as they appear to be critically important. If being 'special' involves being dead, as the article suggests, I'll take being not special please.
3) In order for the life bearing features of the universe we observe to develop, the universe we inhabit needs to be special. Mindbogglingly special.
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