How old is the Universe?

Presented by Miles Hudson

All images courtesy of NASA and Hubblesite.org

This picture shows many galaxies. It

was taken by the Hubble

Space Telescope

But when did it all come into being?

Age of the Universe?

Any guesses?

Three hundred years? 300 y

A thousand years? 1 000 y

Five million years? 5 000 000 y

Two billion years? 2 000 000 000 y

Eight trillion years? 8 000 000 000 000 y

3 x 102

1 x 103

5 x 106

2 x 109

8 x 1012

Maths shorthand

(‘standard form’)

On a scientific calculator, the EXP button means ‘x10’

Did you know that the Universe is expanding?

The light from distant galaxies shows that they are moving away from us.

The Sun

Every galaxy is moving away…

The Sun

Many years later….

So if we run the clock backwards….

Many years ago

The beginning of the Universe

This is the basis of the Big Bang theory.

In 1929, the American astronomer Edwin Hubble did a survey of many galaxies.

He plotted a graph

v(km/s)

How fast it’s moving

How far away it is: d (x1019 km)

and found that the further away a galaxy is, the faster it moves away.

This gave us Hubble’s Law: v = H0d

Hubble’s Law

Hubble’s Law: v = H0 x d

So how fast a galaxy is moving away from us is always so many times how far away it is.

The ‘how many times’ is H0 and is called the Hubble Constant.

And… how old the Universe is can be found from the Hubble constant.

If we follow in Hubble’s footsteps and draw the graph he did, we can find H0 and so we can find out how old the Universe is. Let’s do it!

It’s 1 ÷ H0

Step 1: Draw graph axes Put your paper upright (portrait).

v(km/s)

d (x1019 km)0 1100

(go up in 100’s so 11cm across)0

21000(go up in 1000’smeans 21cm up)

Step 2: Plot the points Galaxy cluster

Distance, d

(x1019km)

Speed, v

(km/s)

Pegasus 120 3800Perseus 190 5200Coma 350 6800Hercules 320 10400

Leo 950 18800Gemini 1100 20600

Step 3: Draw the best fit line through the points

10002000

Finding H0

Finding the gradient, H0

• Pick two points far apart on the best fit line.

• Find the change in v: y• Find the change in d: x• Remember, d is x1019 so put

that on your value for x.• Gradient: H0 = y ÷ x

y

x

v

d

Finding the age of the Universe

Your answer for H0 should be ‘something’ x 10-18

We want to find 1 ÷ H0

Your calculator may have a button marked ‘1/x’ or ‘x-1’. Pressing this will do the ‘1÷’ function we want.

Your answer will be in seconds.

There are 31536000 seconds in one year. So take the number of seconds and divide by 31536000 to find the answer in years.

Remember ‘x109’ means billions.

Alternatively, just type in the calculation with your value of H0.

We’ve used data that Hubble used, and our answer for the age of the Universe is around 16 to 18 billion years old.

Since Hubble plotted his graph, there have been huge improvements in the accuracy of the distance measurements, d.

The current best answer for the age of the Universe is…

. . . 13.8 billion years

13 800 000 000 years

The errors in the data at his time meant that the answer could be anywhere from 10 to 20 billion years.

Download instructions for use, watch the video, buy more rulers, and try more graphing activities, all at …