AAS: Do you think there was anything before the Big Bang?
SH: In the early Sixties there was a big debate as to whether the universe had a beginning a finite time ago. And so, the obvious question was, what happened before the beginning of the universe? As Saint Augustine [an early philosopher] said, what was God doing before he made the universe? He was preparing for all the people who asked such questions!
Does it require a creator to explain how the universe began, or is the initial state of the universe interpreted by a law of science? To answer how the histories of the universe began, Jim Hartle [a professor of physics at the University of California, Santa Barbara] and I proposed what we called the ‘no-boundary hypothesis’. The problem of what happened at the beginning of time is a bit like the question of what happened at the end of the world when people thought the world was flat. Is the world a flat plate with a sea going over the end? I have tested this experimentally. I have been around the world, and I have not fallen off!
As we know, the problem of what happens at the end of the world was solved when people realised the world was not a flat plate, but a curved surface. One can think of the Earth’s surface as beginning at the South Pole, as you head northwards the size of the circles of latitude increase. According to the no-boundary hypothesis, the history of the universe is like this. The history begins at a single point at the South Pole. To ask what happened before the beginning of the universe would become a meaningless question because there is nothing south of the South Pole. Imaginary time, as measured in degrees of latitude, would have a beginning at the South Pole, but the South Pole is like any other point. The same laws of nature hold at the South Pole as in other places. This would prove the age-old objection to the universe having a beginning and that it would be a place where the normal laws broke down. The beginning of the universe would be governed by the laws of science, such as quantum gravity that merges the theories of quantum mechanics – the science of very small things such as particles – with the theory of gravity, which acts over large distances.
AAS: So how do you personally think the universe began?
SH: The universe must have at its beginning a singularity. A singularity is a place where the [solutions to the] field equations of classical general relativity can’t be found. So classical general relativity cannot predict when the universe began.
This was a conclusion with which Pope John Paul was happy! At a conference on cosmology at the Vatican, the Pope told cosmologists that it was okay to study the universe after it began, but they should not inquire into the beginning itself, because that was the moment of creation and the work of God. I was glad he didn’t realise
I had given a paper at the conference suggesting how the universe began. I didn’t fancy being handed over to the Inquisition like Galileo!
Many modern cosmologists are like Pope John Paul. They are happy to apply the laws of physics to the universe after it actually began, but they evade the actual beginning. But in one sense cosmology has no predictive power over what happened at the beginning of the universe. All it can say is that things are as they are now because things were as they were shortly after the beginning. Although classical general relativity predicts that the beginning of the universe was a singularity, at which the theory breaks down, we know that theory has to be quantised like the theories of all other physical fields. Although we don’t yet have a complete theory of quantum gravity, that is how it all works, we have an approximation that is good for practical purposes.
AAS: Has the Big Bang always been the preferred theory?
SH: The prevailing theory used to be that the universe had lasted forever, because something eternal was more perfect, and because that avoided all the questions about the creation. In order to avoid the universe having a beginning, astronomer Fred Hoyle proposed the ‘Steady State’ theory. In this theory, the universe will have existed forever with new matter being continually created as the universe expanded, to keep the density the same. The Steady State theory was never backed up by observation, and had an energy field that was objectionable to particle physicists because it would lead to runaway production of pairs of positive and negative energy particles. But the final nail in the coffin came with the discovery of a faint background of microwaves. These microwaves are the same as those in your microwave oven, but much less powerful – they would heat your pizza only to -271.3 degrees Celsius [-456.34 degrees Fahrenheit]. That’s not much good for defrosting a pizza, let alone cooking it. You can observe this yourself by setting your analogue TV to an empty channel. A few per cent of the ‘snow’ that you see on the screen will be caused by the microwaves.
There was no way the Steady State theory could account for this background. A reasonable interpretation of the background is that the radiation is left over from an early, very hot and dense state – the Big Bang. As the universe expanded, the radiation would have cooled until it was just the faint relic we observe today.
AAS: You have described the universe as a hologram. Could you explain why?
SH: The universe has three spatial dimensions plus time, so it is a four-dimensional object that can therefore be represented as a hologram on a three-dimensional surface. The history of the universe can be represented as a hologram on the boundary of a four-dimensional disc.
As I expect you know, a hologram is a representation of a three-dimensional object on a two-dimensional surface such as a photographic plate. I was supposedly represented as a hologram in an episode of Star Trek: The Next Generation. I say supposedly because although I may have appeared three-dimensional on the Starship Enterprise, television sets at the time could not, and still can’t, display three-dimensional holographic images. That will be the next technological revolution. In the episode I was playing poker with Albert Einstein, Isaac Newton and Commander Data [on the Holodeck]. Because the game was interrupted by a red alert on the Enterprise, I couldn’t cash in my winnings of 140 Federation credits. I approached Paramount Studios, but they did not know the exchange rate!
AAS: What can the cosmic microwave background radiation tell us about the universe?
SH: Cosmology became a precision science in 2003 with the first results from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, which confirmed our simplest predictions of cosmic inflation. WMAP produced a wonderful map of the temperature of the cosmic microwave background, a snapshot of the universe at about three hundred-thousandths of its present age. The irregularities that we see are predicted by inflation and they mean that some regions of the universe had slightly higher density than others. The gravitational attraction of the extra density slows the expansion of that region and can eventually cause it to collapse and form galaxies and stars. So look carefully at the map of the microwave sky and it is the blueprint for all the structure in the universe. We are the product of quantum fluctuations in the very early universe. God really does play dice.
There [was] the Planck satellite, with a much higher resolution map of the universe. The analysis of the Planck data is in remarkable agreement with the simplest models of inflation. All the data suggested that [the fluctuations that made the structures we see today] were sufficient and there seemed to be no need to look for [the first ripples in space-time, or gravitational waves]. Planck only announced a number limit of 11 per cent on [a ratio of gravitational waves to density fluctuations]. Personally I have a bet with Neil Turok, director of the Perimeter Institute, that [this] is at least five per cent. If this is confirmed by future observations, it will be quantum gravity written across the sky.
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