Australasian Science: Australia's authority on science since 1938

## Infinity Equals Nothing

By Simon Grose

**The work of Australia’s new Nobel Laureate challenges the semantics of the absolute.**

Not long after the team led by Prof Brian Schmidt and another group published the work that would win them the 2011 Nobel Prize for Physics (see p.36), another journalist and I shared a congenial lunch with Schmidt at Mt Stromlo Observatory. He talked us through the evidence that the expansion of the universe is accelerating, beguiling us by saying: “The universe is infinite and it is expanding”.

The notion that infinity could be getting bigger was an interesting excursion into relativity (not Einstein’s general version). Dictionary definitions of “infinity” have an absolute tenor to them, like “limitless time, space or distance” or “boundless distance”.

Go to a scientific dictionary and the definitions get mathematical but not necessarily less absolute, like “mathematical quantity that is larger than any fixed assignable quantity”, “the result of dividing any number by zero”, or even the mindbending “minus infinity – a quantity having a value that is less than any assignable value”.

While common dictionary definitions reflect the popular notion of infinity, for astrophysicists the universe defines infinity. Because it is expanding, at any one moment it has a boundary, so it is neither “boundless” nor “limitless”. But because the universe is all there is, it is at least a proxy infinity.

Until 1998, when the Nobel-winning research was published, the opposite understanding held sway. The universe was seen as a finite bunch of matter that erupted from the Big Bang about 13.7 billion years ago. Its expansion after that was believed to be slowing and would eventually reverse to suck all that finite matter back into what Schmidt dubs a “gnaB giB”.

By observing supernovae to calculate the speed at which they were travelling apart, the two Prize-winning teams were seeking to set a date for the gnaB giB by coming up with a value for q0, the deceleration parameter for the universe.

They found the opposite of what they had been expecting, so they questioned their data. All theory and belief told them that they had made an error, but their observations and their inevitable conclusion withstood scrutiny – now affirmed by the Nobel jury.

So it could be said that in the late 1990s the universe flipped from being finite to being infinite – a momentous reversal that shows, among other things, how rudimentary is our understanding of things cosmic.

It also tells us that the universe will end with neither a bang nor a gnab – it will never end. This infinite thing will just keep expanding. As all its components spread more distant from each other, light and heat discernable from any vantage point will diminish and ultimately reach zero. A virtual observer from any vantage would thus perceive nothing – an ironic conclusion to an expanding infinity.

What was that about “minus infinity”?

Simon Grose is a Director of Science Media (sciencemedia.com.au).