The universe and beyond

by Rebecca Priestley / 21 July, 2012
A cosmologist answers questions about the nature of light and how many dimensions there are.


My last Q&A column, in which University of Auckland physicist and cosmologist Professor Richard Easther answered questions about the speed of light and the expansion of the universe, inspired several Listener readers to write in with “questions for Richard”.

Basil McCoward from Napier is puzzled by the dual nature of light, which is known to behave like a particle and a wave: “As I look out my window, rays of light are impinging on my eyes, reflected from sunlight striking buildings, verdure, fences, and animals, to form a clear picture on my retinae. Many more rays are being reflected in every direction. I know that light can behave like a wave, and waves can interfere with one another. “The famous twin-slit experiment seems to prove that even a single photon, passing through one slit, can create interference bands on a screen, appearing to actually interfere with itself. Why and how is it that all those millions of rays or particles do not bang into each other?”

“You are right,” says Easther, “these rays do overlap with each other. Interference patterns form when waves overlap and cancel each other out. On a sunlit day, there will always be spots where all the different light-waves add to zero, just as there are spots on a choppy sea where the water level exactly matches the height it would be on a calm day. “But each cancellation only lasts for a fleeting instant and is thus unseen. One way that you can see this interference is by shining a laser pointer at a painted wall – look closely at the spot of light on the wall, and it will be a pattern of dots called ‘laser speckle’. The light rays from a laser are all in phase, like marching soldiers or a troupe of dancers, so always cancel each other at the same points, leading to a visible pattern. “As for ‘banging into each other’, when you see an interference pattern it’s a wave collision, not a particle collision. Light particles, or photons, don’t interact unless they have an enormous amount of energy – far beyond the range of visible light.”

Andrew Bydder from Hamilton asks: “How many dimensions make up the universe?” “One time and three space, so far as we know. Many theories of fundamental physics – most famously string theory – suggest that space has extra dimensions (beyond the usual up-down, front-to-back and side-toside) that are somehow hidden from us. This might be because they are so tightly curved we cannot probe them, or that our 3D universe is a ‘brane’ – a giant 3D ribbon in a higher dimensional space – and the particles we are made of cannot escape from the brane, so we only see a 3D world. “There is no experimental evidence for these propositions – but the idea that our universe has extra dimensions is remarkably old – it was discussed in detail by European physicists Theodor Kaluza and Oskar Klein in the 1920s.”

Easther watched the recent transit of Venus from the sixth floor of the University of Auckland physics building. But for Easther and his fellow cosmologists, things like planets and stars, no matter how rare the astronomical event, “are mainly foreground, things we have to look past to see what we want to see”. The next big event on the cosmological calendar, says Easther, is in January 2013, when processed data from the Planck Satellite survey of the microwave background radiation will be released, yielding a picture of the universe before the stars and galaxies formed. Cosmologists will be “sitting on the edge of their seats”, he predicts.



Send questions to science@listener.co.nz
MostReadArticlesCollectionWidget - Most Read - Used in articles
AdvertModule - Advert - M-Rec / Halfpage

Latest

Everything's shipshape: A visit to a Viking ship burial
71738 2017-04-28 00:00:00Z Travel

Everything's shipshape: A visit to a Viking ship b…

by Heather Whelan

Ladby is Denmark’s only ship grave; it is also the only place in the world where a Viking ship burial can be visited.

Read more
Women in tech: Why the industry needs to fix its gender problem
71822 2017-04-27 15:48:38Z Technology

Women in tech: Why the industry needs to fix its g…

by Max Towle

Just under one in three IT grads in 2015 were women. But it’s not quite translating to the industry.

Read more
We shouldn't forget immigration is cyclical, too
71818 2017-04-27 15:21:44Z Social issues

We shouldn't forget immigration is cyclical, too

by The Listener

As we debate the “Goldilocks” size of our population, it's timely to remember that only five short years ago NZ was lamenting its net migration loss.

Read more
Who’s the We? Maori, Pakeha and an anthem's bonds of love
71511 2017-04-27 00:00:00Z History

Who’s the We? Maori, Pakeha and an anthem's bonds …

by North & South

'In the bonds of love we meet', goes our anthem. But who's the 'we'? Do modern histories focus too much on a clash between Maori and Pakeha?

Read more
Kaye expects 'healthy debate' over Te Reo in schools
71629 2017-04-27 00:00:00Z Currently

Kaye expects 'healthy debate' over Te Reo in schoo…

by RNZ

Any extension of teaching Te Reo in schools would depend on whether the resources are available for it, the incoming Education Minister says.

Read more
How Arthur Conan Doyle came to create Sherlock Holmes
71313 2017-04-27 00:00:00Z Books

How Arthur Conan Doyle came to create Sherlock Hol…

by Abbie Read

A new book tells how investigative chronicler Sir Arthur Conan Doyle came to create his famous private detective.

Read more
Book review: The Earth Cries Out by Bonnie Etherington
71595 2017-04-27 00:00:00Z Books

Book review: The Earth Cries Out by Bonnie Etherin…

by Paula Morris

A debut novelist finds inspiration in her New Guinea childhood.

Read more
Auckland comedian Angella Dravid is about to blow up
71651 2017-04-27 00:00:00Z Arts

Auckland comedian Angella Dravid is about to blow …

by Rosabel Tan

Polite, warm, but generally anxious, comedian and Billy T nominee Angella Dravid is still searching for the punchlines in her upcoming solo show.

Read more