Horizon - How Big is the Universe?

[Hot Soup]

http://www.bbc.co.uk/iplayer/episode..._the_Universe/

that was a cracking watch, a much used phrase but - Mind Blowing.

Recommended.

[stepper]

Sensational - the pictures of the Milky Way in the first 5 minutes had me hooked.

My brain hurts just trying to comprehend it all

[PsYcHoKiLLa]

...and yet people still believe we came from a magic man in the sky. Also how can anyone not believe there is no other intelligent life in all of that?!

It's almost impossible to say. The standard way to think about the probability is to look at all the independent factors that are necessary for extraterrestrial intelligence, assign a probability to each, and multiply out to determine the probability that an extraterrestrial intelligent civilization exists. Note that this assumes all civilizations are like ours - existing on Earthlike planets etc.

The relevant factors are:
N* - the number of stars in the galaxy (or the universe).
f_p - the probability that a given star will have planets.
n_e - the number of Earthlike planets a given planetary system has
f_l - the probability that one of these planets will develop life
f_i - the probability that this life will become intelligent
f_c - the probability that this intelligence will be able to communicate
L - how long this civilization sticks around
T_g - how old the galaxy is - so that we estimate the number of intelligent civilizations that currently exist, rather than counting those that disappeared

The Drake Equation, used to estimate the number of ET civilizations, just says that [math]E(# of ET civilizations) = N^{*} \cdot f_p \cdot n_e \cdot f_l \cdot f_i \cdot f_c \cdot L / T_g[/math]

Some of these values are known -
N* ~= 100B stars
T_G ~= 10B years
f_p seems to be 20-60%
n_e is estimated at > 0.005;
f_l has been estimated at > 0.13, based on how long it took life on Earth to develop
f_i, f_c, and L we have no data on - Drake estimated these at 0.01, 0.01, and 10,000 years respectively

Plugging these into our equation*, we get that the expected number of ET civilizations in our galaxy is 0.26.

For more detail, see http://en.wikipedia.org/wiki/Dra...

*These are the values I'm using; f_p = 40%; n_e = 0.005; f_l = 0.13; f_i = f_c = 0.01; L = 10,000

So the probability is there are around 10,000 intelligent civilisations in the known universe.

http://www.quora.com/Extraterrestria...ligence-exists

The thing that amazes me is a lot of the stars we see in the sky probably don't exist because the light from them takes so long to get to us that they've probably gone supernova so the night sky you're looking at doesn't even exist, like some cosmic mirage.

[Dave]

Superb watch, cheers

[GroovYF]

Forgot it was on, but will iPlayer this.

[*XeR0x*]

Anyone been watching the James May programme afterwards?

It's been pretty good at explaining scientific stuff

[GroovYF]

Watched Horizon last night...