The universe seems to be full of matter and energy, both the same thing really since matter and energy are inter-convertible according to Einstein's equation E=MC2, where E is energy, M is matter and C is the speed of light. If you added up all the energy, you might expect to get an enormous total. However, the amazing thing is that if you do this calculation the answer is zero - the universe contains nothing and therefore could have arisen from nothing in the beginning!
Gravity is a form of negative energy. The other energy in the universe is positive energy in the form of mass and forces that keep matter particles apart. If you do the sums it turns out that all the positive energy in the universe is precisely cancelled out by all the negative energy.
In order to help to visualise this, consider the following. You have €20,000 on deposit in the bank, but you also owe €20,000 to the Mafia. Your net worth is zero. In a similar way, the universe contains both positive and negative energy and both types cancel each other out when you do the sums.
When you look at the night sky you see millions of stars and between them, the blackness of space. We call this blackness the vacuum and we are accustomed to thinking that it is empty. But modern physics tells us that the vacuum is not empty.
The ancient Greeks declared that matter is composed of tiny indivisible particles called atoms. In order to account for motion the Greeks also postulated the existence of a void through which the atoms can move. Atoms were things and the void, or vacuum, was nothing. But, if the vacuum is nothing how can it be said to exist?
Also, how can we speak about the universe as a whole if we see it as being shot through with a vacuum that is non-existent? Such a universe would constitute not a unity, but many realms, separated by the non-existent. This problem was recognised by Aristotle, Plato and others.
Most physicists in the 19th century believed that the vacuum was filled with a ghostly substance called the ether. The famous Michelson-Morley experiment (1881) failed to detect the ether and in the early 20th century, Einstein showed that the ether is also theoretically superfluous.
But no sooner was the vacuum emptied of content than quantum theory, developed early in the 20th century, filled it up again. One of the rules of quantum mechanics is called Heisenberg's Uncertainty Principle, which states that if you know where a subatomic particle is, you cannot know how fast it is moving, and if you know how fast it is moving you cannot know its position.
In order to measure a particle's energy or mass to a given degree of accuracy, you need to observe it for a certain length of time, with the shorter the time the more uncertain the measurement. If the time is extremely brief, the uncertainty becomes greater than the particle's mass and you cannot say for certain whether the particle is there or not.
On very short time-scales, the rules of quantum physics allow subatomic particles to exist briefly even in the vacuum. The particles and their corresponding antimatter particles pop in and out of existence, arising out of the vacuum and disappearing again before the universe notices their presence.
The less energy involved in a quantum fluctuation, the more time the virtual particle can exist before it must vanish. Given enough time, a quantum fluctuation in the vacuum will produce a particle/antiparticle with a perfect balance of positive and negative energy and zero net energy.
These particles could last forever and the quantum fluctuation could instantaneously inflate to enormous size, with positive matter energy inflating at the same rate balanced by negative gravitational energy and the total energy remaining zero.
In the 1970s, a few cosmologists formulated the idea that the entire universe may have begun as a quantum fluctuation in the vacuum. The rules of quantum physics also say that, in this event, the universe started out as a particle one hundredth of a billionth of a billionth of the size of a proton and infinitely dense and hot. At this enormous energy, all of the forces of nature (gravity, electromagnetic, strong and weak nuclear forces) were combined as one force.
Gravity quickly separated out as a discrete force and the other forces followed rapidly. The splitting apart of the forces converted some of the available energy into an enormous outward push and the universe started to expand dramatically. This dramatic expansion is called inflation.
In a tiny fraction of a microsecond, the universe expanded, creating positive matter energy and negative gravitational energy as it went, to about the size of a grapefruit and at that stage contained all the matter and energy present in the universe today.
At that point, all the forces of nature had split apart and the exponential expansion stopped. However, the universe continued, and continues, to expand at a more sedate pace.
The universe may be nothing more than the ultimate quantum fluctuation. As a wit once remarked: "In the beginning there was nothing, which exploded."
William Reville is a ssociate professor of biochemistry and director of microscopy at UCC
