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 Moon crosses the celestial equator on the 22nd, 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 23rd.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton.























Just Posted

Keremeos man says stem cell therapy changed his life

Darryl Brewer says he went from being immobile with chronic pain to leading an active lifestyle

Penticton resident’s dog allegedly stolen from construction site

Nicholas Bozak is seeking the public’s assistance in locating Askem, his 17 month old mastiff chow

Experience the music at the 97 South Song Sessions in Penticton

Songwriters Tim Nichols, Jimmy Yeary, Jessica Mitchell and Bob DiPiero to perform intimate concert

Okanagan-Shuswap weather: cloudy, showers expected

Environment Canada is predicting a mix of sun and clouds tomorrow and a sunny weekend across the Okanagan

Okanagan society sends seniors, shut-ins on boat excursions

Okanagan Quality Life Society has been providing Okanagan Lake boat rides for nearly 30 years

Feds lowered poverty line, reducing the number of seniors in need: documents

Liberals introduced a poverty line that was below the prior low-income cutoff

Luxury home auction kicks off in Lake Country

Questions circle around how an unreserved auction will work

$900M settlement reached in class action on sexual misconduct in Canadian military

After facing criticism, the government moved to begin settlement proceedings in early 2018

Tax take stays ahead of increased B.C. government spending

Tax revenue $2.1 billion higher than budget in 2018-19

Two toddler siblings found drowned on First Nation in Alberta

The siblings were found drowned on their family’s property, according to RCMP

Chiefs honour Indigenous leader wrongfully hanged in B.C. 154 years ago today

Chief Joe Alphonse says they want his remains returned to his homeland in B.C.’s Cariboo region

Lightning strike sparks fire outside Kelowna

BC Wildfire is reporting a small blaze off Highway 33

RDOS construction activity shows increase

264 permits, worth nearly $26M, have been issued in first half of 2019

Snowbirds touch down in the South Okanagan

Canadian Forces Snowbirds make pit stop in Penticton

Most Read