Reflections on the Size of the Universe

I believe the Hubble deep field images are among the most awe inspiring photographs ever taken and I have recently set the Ultra Deep Field up as my desktop background. To take this image the Hubble telescope was pointed at an area of space devoid of  nearby stars and an image of deep space was constructed by accumulating data over a period of several months. The total area encompassed is equivalent to a speck about one millimetre squared held at arms length. Yet this tiny tiny window on the universe is crammed full of galaxies. Each of these galaxies likely has billions of stars. This image contains some of the farthest away objects ever observed - galaxies at a remove of billions of light years from our own.

This number of worlds, these distances, these time-scales are completely mind boggling. They are in truth simply unimaginable and yet they exist. Here is the picture:

 

(Image in the public domain courtesy of NASA. A high resolution version can be got from Wikipedia )

One thought that immediately strikes me as I contemplate this picture is how inconceivable it is that our humble sun is the only place in all of this immensity where the miracle of life came about. The universe must teem with life, just as it teems with stars. Why then have we not heard from any one else?  Science fiction writers have proposed many reasons ranging from the benign (our development is being quietly observed from afar until such time as we are judged fit to join the congregation of space faring races) to downright scary (some malevolent force  systematically eliminates all space-faring races).  Could it be that life evolved elsewhere is so fundamentally different as to be unrecognisable to us or is it  simply due to the immense distances involved and the tyranny of the un-attainable speed of light?

The second thought that strikes me is how this immensity exposes the arrogance of that branch of human science known as cosmology. Hypotheses such as the big bang, black holes and dark matter are afforded the same respect as established scientific fact when they are really no more than extrapolations built upon extrapolations. Extrapolation is a useful tool that allows us to use those things we know to make predictions about those things which are outside of our current scope of knowledge. However every extrapolation incurs uncertainty and the further we go from the dataset of the known the greater the uncertainty.  Thus knowledge gleaned on Earth of how things move and interact had a reasonable chance of holding up when extrapolated  to the neighbouring planet of Mars and indeed the experience of the Mars landers has shown that the extrapolation was valid. Cosmologists extend such extrapolations a billion billion times further though and the uncertainty becomes so large as to render the extrapolations completely useless. 

There is nothing new about this - every era has had its cosmologists who confidently claim to have the full and true explanation of the universe. Just as today the proposers of such theories have often been held up as mystical geniuses safe in the knowledge that no one was likely to be able to prove them wrong. This is not science. It is closer to religion than science and indeed it was real evidence based science that eventually exposed the cosmic eggs, the celestial spheres and the epicycles for the failed extrapolations that they were. I will therefore make a bold extrapolation of my own: I believe that in years to come the cherished cosmological hypotheses of today will similarly perish beneath the ongoing march of real evidence based science and children of a future age will look back and chuckle at our big bangs and black holes with much the same amusement that we feel when considering Ptolemy's epicycles.