STARGAZING: How big is the universe?

Visitors to our observatory often ask this seemingly obvious question. How big is the universe?

Visitors to our observatory often ask this seemingly obvious question. How big is the universe?

We know how long it has been since the Big Bang, when the universe started to expand from something infinitesimally small: about 13.8 billion years. If we can quote a number like that for the age of the universe, it is logical that we should have as good a number for the size of the universe. However, that is a tougher question.

Picture us living on the surface of an expanding bubble. If we imagine stars and galaxies scattered all over its surface, we would see them all being carried away from us by the expansion, and the further things are from us, the faster they will be receding. However, if we start travelling over the surface of our bubble universe, we will never encounter an edge; we will eventually be back where we started.

For the sort of distances we have here on Earth, we can neglect the amount of time taken for light to travel from an object to our eyes.

In a millionth of a second light travels 300 metres. We see an object that far away as it was a millionth of a second ago. We can forget that tiny delay. However, once we get into space the distances get larger, and the times become noticeable. We see the Moon as it was 1.25 seconds ago, and the Sun as it was eight minutes ago. The time delay for the nearest star after the Sun is 4.3 years. We see Capella, that star glittering in the northern sky on late summer evenings as it was 42 years ago. Kilometres, millions or even billions of kilometres, are too small to be useful units of distance for astronomy.

One of the units we use is the light year. This is the distance light travels in a year, which is a little less than 10,000,000,000,000 km. Therefore, if the radiation from the Big Bang started on its way to us 13.8 billion years ago, so at that time the radius of the universe must have been 13.8 billion light years. We call that the size of the Observable Universe. However, during the time those light waves were travelling to us, the universe has continued to expand. We cannot update the size of the observable universe because that light has not reached us yet. However, from measurements of the expansion of the universe for objects we can see, the radius of the universe today is something like 46 billion light years. That is a diameter of about 92 billion light years.

There is no way we can yet see light from that more modern universe; it is still on its way to us. The light now starting on its journey should arrive in around 32 billion years.  By that time of course that number will be too small. Moreover, that still will be just the size of the patch of universe we can see, not the full size of it.

We have always taken the word Universe to refer to the summation of everything there is. Obviously, if this were the case, there would be no meaning to the possibility of anything else. However, the problem is not with the word; it is with us. A few centuries ago, the Universe consisted of the Earth, with everything we see in the sky being part of the heavens. Until well into the 20th Century, the universe was taken to be only our galaxy. Then when other galaxies were discovered, for a while they were referred to as Island Universes. Eventually there was one thing we call the Universe, which started 13.8 billion years ago.

Now there is some evidence of our universe being just one of many, forming like bubbles in some great, multidimensional cosmic foam. When I was reading astronomy books on the bus taking me to high school, I read that it was unlikely if we would ever know for sure about the Big Bang.  So much for that! What will we know in a decade or two?

The Sun crosses the celestial equator on the Sept. 22, marking the Autumn Equinox. Venus lies very low in the predawn sky; Jupiter rises in the early hours. Saturn and Mars lie close together in the sunset twilight. The Moon will be New on the Sept. 23.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.Tel (250) 497-2300, Fax (250) 497-2355E-mail: ken.tapping@nrc-cnrc.gc.ca

 

Just Posted

This photo of the small wildfire burning above Naramata was taken at 8 p.m. on Thursday, June 17, 2021 (Monique Tamminga Western News)
BC Wildfire on scene of small wildfire above Naramata

Black smoke can be seen rising from the mountain

Keremeos’ heritage Grist Mill and Gardens. (Brennan Phillips - Keremeos Review)
Keremeos Grist Mill looking forward to restrictions easing with exclusive concert planned

Juno Award-winning folk artist Valdy is set to take the stage

Letter writer says COVID has created lots of newbie cyclists who don't know rules of cycling. (File photo)
LETTER: Newbie cyclists in Penticton need lessons on rules of the road

Penticton cycling group just received city funding, should give back by offering how-to lessons

No dental coverage for low income Canadians. (File photo)
OPINION: Penticton MP’s proposal for universal dental coverage rejected

One in 3 Canadians have no dental coverage, with COVID making it even worse

The weekly COVID-19 map for June 6 to 12. (BC CDC)
South Okanagan sees only 5 new cases in last week

The Similkameen Valley went a second week without any new cases

Bear wanders Kelowna on June 15. (Michelle Wallace/Facebook)
Bear climbs fence, uses crosswalk in Kelowna

The bear was spotted on Baron Road Wednesday evening

Hundreds of people, young and old, joined the three-day Walking Our Spirits Home procession, honouring residential school survivors, those who never made it home and all those affected by the institutions. Here people walk the third portion on June 13. (Martha Wickett - Salmon Arm Observer)
Walking Our Spirits Home from Kamloops provides path to healing

First Nations in and beyond Secwépemc territory join in to honour residential school survivors

More flames
Lake Country home destroyed in large blaze, 11 dogs rescued

Fire crews are responding to 10839 Hallam Drive

(Facebook/Kelowna Cabs)
Kelowna Cabs reaches tentative agreement with dispatchers union

The tentative agreement could help end the dispute between the taxi company and the dispatchers

FILE – A science class at L.A. Matheson Secondary in Surrey, B.C. on March 12, 2021. (Lauren Collins/Surrey Now Leader)
Teachers’ union wants more COVID transmission data as B.C. prepares for back-to-school

BCTF says that details will be important as province works on plan for September

A boat sharing service is extending to Summerland. The company, Penticton Boat Club and Rentals, is also taking over the boat rentals at Summerland Waterfront Resort. (Photo by Chris Stenberg)
Boat sharing service extended from Penticton to Summerland

Company will also operate boat rentals at Summerland Waterfront Resort

201 First Street West 1980s. Prior revitalization. (Photo from Revelstoke Museum and Archives)
Man who redesigned downtown Revelstoke honoured with lifetime achievement award

Robert Inwood has worked on historical projects across the province

Provincial health officer Dr. Bonnie Henry outlines B.C.’s COVID-19 restart plan, May 25, 2021, including larger gatherings and a possible easing of mandatory masks on July 1. (B.C. government photo)
B.C. records 120 new COVID-19 cases, second vaccines accelerating

Lower Pfizer deliveries for early July, Moderna shipments up

Most Read