In a rare opportunity to speak to one of Britain's greatest living scientists we decided to ask the Astronomer Royal, Lord Rees, the big questions: is there extraterrestrial life out there, are there other universes and what came before the Big Bang?
Martin Rees, who was president of the esteemed Royal Society until 2010, has made many significant advances in Cosmology over the years, including his study of Quasars which, indirectly, led to the final disproof of the Steady State theory.
I was working with a supervisor who was a cosmologist and we discussed whether there was evidence against the Steady State theory. The discovery of objects at very great distances such as Quasars allowed one to compare the universe today with the universe a long time ago to see if it was different in the past from now. We highlighted one of the first bits of evidence that things were different in the past which was incompatible to the Steady State theory but of course quite compatible with an evolving universe where galaxies might indeed have been more prone to explode in the past than now.
First of all, I prefer the term Anthropic reasoning, it's not really a principle. The idea there is that perhaps we are in a universe which is a subset of all possible universes but is one of the subset in which complexity can arise. We shouldn't be surprised if we are not in the kind of universe that is empty of matter, has no gravity, or is very small. There are some cosmological theories which permit the existence of a huge range of universes. We then have to ask, are we in a typical member of the subset in which we could exist rather than being a typical member of the ensemble?
This is something I've worked on for a number of years but it is of lively interest because some of the best or most popularly believed theories of fundamental physics suggest that in fact the laws of nature have a certain arbitrariness in them and could be different. We then have to ask why we are in a universe where the laws have a particular form.
The concept around Anthropic reasoning is one way to deal with this. To give an analogy, if there was only one planet in the universe, you might be surprised that it is a planet that allows life to exist because it's orbiting a long-lived star at a distance such that water neither boils nor freezes. But now we know there are zillions of planets we are not surprised that some have these conditions and we are one of that subset.
The important discovery in the last decade or so is that most stars do have retinues of planets orbiting them just as the sun has the familiar planets going around it. This was speculated before but the evidence only emerged recently. Many of those planets are like the Earth and that of course makes one wonder if they would have life on them as the Earth does.
We still can't answer that question because we can't get direct evidence of whether there's a biosphere of these other planets but I hope that in the next 20 years or so we will be able to answer this question more definitely in one of two ways: either we will be able to find some evidence that there is life elsewhere by astronomical observations or, through advances in biochemistry, have a better idea of how life began here on earth because that is a problem which still perplexes all biologists. If we understood how life began here on Earth we would then know whether it was via some rare fluke or whether it was via some process that would be expected to have occurred in the same way in a similar environment on another planet.
They've been discovered in the last few years and there are two techniques which are used. One is by observing very carefully the star and finding that its motion wobbles a bit due to the gravitational pull of a planet going around it. And the other technique is the so called transit method, where one monitors very, very accurately the brightness of the stars and looks at the slight dimming that would occur if a planet moves across in front of it, blocking out a bit of light.
This latter technique has been done by the Kepler spacecraft which, for the last three years, has been monitoring the brightness of 150,000 stars with a precision of 1 part in 100,000. And it repeats all that several times an hour.
Well, what is remarkable is that we can now trace cosmic history back with a fair degree of confidence to a time when everything was squeezed to a density higher than in an atomic nucleus and when everything was expanding in a timescale of about a nanosecond. We trace things back with confidence to there. Now, you then ask, what happened even before that and of course a great deal probably happened before that time but that is more uncertain because the further you extrapolate back towards the very beginning, the more extreme the conditions get: the denser, the hotter, the more energetic.
Therefore we have less certainty about them because conditions are more extreme than we can simulate in the lab here on earth. The physics of the very, very earliest stages is less confidently understood so we don't quite know. However, it is amazing that over the last 40 years we have changed from not being quite sure if the universe is evolving at all to being able with confidence to trace it back to when it was only a nanosecond old. That's about 13.7 billion years ago.
But every advance leads to the development of a new set of questions and the current fundamental questions are to understand why it's expanding the way it is, why our universe contains the particular mixture of radiation and atoms and dark matter that we observe. It is an ongoing quest but we are making a great deal of progress so there are lots of ideas about the very beginning and one hopes in the next forty years some of them will firm up. Incidentally, when we do have a better understanding of the earliest stage of the Big Bang we will be able to say with more confidence whether our Big Bang was the only one or whether there were others as well, like in the multiverse concept.
As we go back in our minds towards the very beginning, the conditions, as I mentioned, get more extreme and we have to jettison more and more of our common sense concepts. Quantum effects are very counter intuitive, and when we get right back to the very beginning the whole idea of 3 dimensions of space and one of time, may have to be abandoned or generalised in some way. If we have to abandon the idea of time as a dimension ticking away then the whole concept of 'before and after' gets a bit fuzzy. The question of how we embed our concept of the Big Bang in some empirically tested fundamental theory is certainly a challenge for the future.
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