The age of the universe on stargazing live.

[paler31]

I was watching Stargazing live last night and they were talking about the expansion of the universe and quoted the Hubble constant which describes the expansion of the universe as 70km/s/Mparsec. Apparently from this figure you can determine the age of the universe. Here is what I did to determine the age of the universe from this figure.

Firstly I converted Mparsec into km. Now the speed of light in a vacuum is quoted as 299792458 m/s now the number of seconds in 1 year is 60x60x24x365.25 = 31557600s therefore light will travel a distance of 299792458 x 31557600 = 9.46 x 10¹⁵ m = 9.46 x 10¹²km in 1 year.

Now 1 parsec is a distance of 3.26 light years therefore 1 parsec is a distance of:-

3.26 x 9.46 x10¹²= 3.08 x10¹³km so a Mega Parsec is 3.08x10¹³ x 1x10⁶= 3.08 x10¹⁹km

We can now wright Hubbles constant as 70 km/s/3.08x10¹⁹km now the km cancel out and you are left with 70/3.08x10¹⁹s = 2.27x10^-18/s Putting this figure into 1 should give the age of the universe so we have the universes age as 1 / 2.27x10^-18 = 4.41 x10¹⁷s and we already know there are 31536000s in 1 year therefore the age of the universe is 4.41 x10¹⁷ / 31557600 = 1.40 x 10 ¹⁰ years or 14 billion years. Now they said that this calculation should yield a figure of 15 billion years so where have I lost my billion years from can anybody spot it or explain how to do this calculation properly? I cant see any errors in my logic but I am sure I must be doing something wrong.

[studdedsole]

I don't think the Hubble constant is considered absolute as it varies according to the model adopted to map the contents of the universe, (matter, energy and radiation). As a result there is a range of values dependent upon the model employed.

The range of the Hubble constant is commonly held to be between 65 and 80km/s/Mpc.

The age of the universe is 1/(Hubble Const) yielding a value between 15.4 and 12.5 billion years.

Your calcs look sound so maybe it was slip of the tongue.

The commonly held "best" value for the Hubble constant appears to be 72km/s/Mpc which yields 13.9 billion years.

Over to the cosmologists

[starnut]

That's all very well, but was it done over six days

[studdedsole]

That's all very well, but was it done over six days

That's only about error of 10ˉ¹² over 14 billion years

[cantab]

I agree. I just put in 1 / (70 km/s per Megaparsec) into Google, it does all the unit conversions for you, and yeah, 14 billion years, not 15. I suspect the issue has already been extensively hashed out over Twitter though. To get 15.0 billion years one would have to use a Hubble Constant of 65 km/s/Mpc, not 70.

[paler31]

Thanks for the reply's Not sure of the significance of six days though. On the program he quoted the Hubble constant at 70km/s/Mparsec so how people managed to work it out at 15 billion instead of 14 billion is beyond me. I may have to tweet him and tell him he is wrong.

John

[studdedsole]

Thanks for the reply's Not sure of the significance of six days though. On the program he quoted the Hubble constant at 70km/s/Mparsec so how people managed to work it out at 15 billion instead of 14 billion is beyond me. I may have to tweet him and tell him he is wrong.

John

I presumed 6 days was a tongue in cheek reference to the creationist theory where Moses said the world was created in 6 days, however God does things simultaneously and this magnitude is used to gain an order for the creation of the world.

[bomberbaz]

The creationist theory would be great if it were true. Then he could start over in a Trillion years or so once all life is extinct in the universe, that way we all get our second chance, or maybe our third, fourth or millionth etc

Its all very deep and a little dark once you go into it you know

[JamesF]

I don't think the Hubble constant is considered absolute as it varies according to the model adopted to map the contents of the universe, (matter, energy and radiation). As a result there is a range of values dependent upon the model employed.

The range of the Hubble constant is commonly held to be between 65 and 80km/s/Mpc.

The age of the universe is 1/(Hubble Const) yielding a value between 15.4 and 12.5 billion years.

Your calcs look sound so maybe it was slip of the tongue.

The commonly held "best" value for the Hubble constant appears to be 72km/s/Mpc which yields 13.9 billion years.

Over to the cosmologists

In the programme they explicitly asked people to work with a figure of 70km/s/Mpc.

James

[JamesF]

That's all very well, but was it done over six days

And about 6000 years ago?

James

[yerodretep]

I can't get to 15 billion years either using 70km/s/MPc.

More like approx. 14 billion years.

Probably live TV, most of us could forget of our names under that pressure unless use to it LOL !

Also Quintillion is not about 10^10 by order of 10^8!

(assuming the short scales here)

Million=10^6

Billion=10^9

Trillion=10^12

Quadrillion=10^15

Quintillion=10^18

Sextillion=10^21

Septillion=10^24

Octillion=10^27

Google=10^100

Centillion=10^303

Googlplex=10^Google

etc to

Graham's NuMber & Beyound!?

upto Grahams Number

[spurius]

Holy Rubbish! You guys are incredibly brainy, I couldnt come up with half that stuff if I lived to my 1st birthday on neptune.

[studdedsole]

Holy Rubbish! You guys are incredibly brainy, I couldnt come up with half that stuff if I lived to my 1st birthday on neptune.

We're just a bunch of old saddos

[yerodretep]

Also current measurements that were mentioned on a previous programme (Maybe Brian can't recall which just yet), said that space is flat, but the degree of precision for this wasn't that big, maybe 2 or 3 dec pl., so may be it's very slightly curved and actually not inifinite (beyound our concepts)!!

[stellarpunk]

I concur (and I teach Physics!). If you use 70 km/sec/Mparsec then I got 13.8 Billion years (to 3 sig fig). No idea at all what [removed word] Brian was wittering on about...

That being said, I do like him but he's not immune from being Mr Wrong at times... this isn't the fist occasion...

[stellarpunk]

Ohh I've been censored! Bad bad stellarpunk

[M06Abe]

13.78 Billion years old ? Give or take a few mistakes,.. And this is only applied to the observable universe. How could we measure something we can't see ? (Excluding Black Holes lol)