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Friday, 18 January 2019

Light & Dark


The BBC showed an interesting two-part documentary recently called Light & Dark. I always enjoy Professor Jim Al-Khalili’s excellent science programmes on TV and radio. 
learned one especially interesting scientific fact when I watched the second part last night. We know that light travels in straight lines, right? (If you didn’t know that – you do now!). We also know that there are about 10 billion galaxies in the universe and that there are around 100 billion stars in the average galaxy. That gives us a total of about 1 trillion billion stars. So: every point of the sky should be lit up and the sky ought not to be dark. Obviously the photo shown here was taken by a very powerful telescope and has about, what, 5% of the sky lit up. It was once thought that dust clouds in space were obscuring our view of the others but we now know that that isn’t the case.
The reason is that a mere 200 million years after the Big Bang, 13.7 billion years ago, the first stars began to form – and the light hasn’t reached us yet! I find that astounding and it makes me feel very small and insignificant...
I’m listening to Chris Bell’s 1973 song 
You and Your Sister. It’s just the kind of plaintive pop song I go for. Listen HERE.
Although Chris was killed in his sports car in 1978, at the age of 27, he was very influential on later musicians.

13 comments:

Susan Flett Swiderski said...

I used to be a pretty darned good physics student many years ago, but when I read some of Hawkings' work, I realized how little I knew and understood. Even so, it's a fascinating topic to study and a great way to remain humble.

I'd quibble a teensy bit with you statement that light always travels in a straight line. Photons travel in a straight line, but the path of light itself can change, depending on the medium through which it travels. For example, in applications using fiber optics, scientists can alter the light beam's path by changing the makeup of the glass through which it flows. In essence, they can "bend" the path.

Then again... maybe my understanding is a bit "off." (Wouldn't be the first time!)

Parnassus said...

Hello Bazza, In college, I started out as a physics major, but veered off course (apparently like some photons). The fact that the ends of the universe are "out of communication" with each other is fascinating and has many implications in astrophysics. --Jim

Joe said...

If the first stars began to form as much as 13.7 billion years ago, that will explain why the light hasn’t reached us yet. But imagine how flooded with light our earth will be, once the light does reach us.

Starting Over, Accepting Changes - Maybe said...

Science was never my forte and I truly have been in the dark most of the time when people try to enlighten me. I still have nightmares about being in chemistry and physics classes many years ago and trying to be invisible to the teacher. I just know what I see and there is nothing that is more beautiful and awe inspiring than a star filled sky on a summer evening.

I don’t remember that song or singer but I enjoyed listening to it very much. Thank you, Bazza.

NanaDiana said...

Light years always amaze me -knowing how long it takes light to reach us from "out there". Great post, Bazza. I hope you have a great weekend. Diana

bazza said...

Susan: OK, but can we agree that light APPEARS to travel in a straight line? Obviously it depends on the medium through which it travels And gravity. And it CAN bend by itself. OK: light doesn't travel in a straight line....

bazza said...

Jim: As Roger Penrose has said, it's rather hard to conceive of the fact that the universe might not be finite or have had a state before the Big Bang. I'm suddenly feeling out of my depth!

bazza said...

Joe: Absolutely! You have neatly encapsulated the essence of this post. It's an astonishing thought that is difficult to truly comprehend for us mere humans...

bazza said...

Arleen: I enjoyed science at school but wasn't much good at it. I was much better at Art and English.
I'm glad you liked the song. Chris Bell was a founder member of Big Star and sang Thirteen - another big favourite of mine. Search 'Big Star Thirteen' on You Tube!

bazza said...

Diana: And even more amazing - light from the early universe hasn't got here yet after all that time. Have a great weekend yourself!

klahanie said...

Hey Bazza,

I've been fascinated with all things astronomical since astronomers discovered rings around Uranus.

Of course, everything we see happened in the past. Unless we consider that past, present and future are simultaneous. Thank you for this post.

Gazza!

bazza said...

Hi Gazza. Always good to hear from you. It's kind of difficult to gets one's head around the idea of space, time and energy being different aspects of the same thing. As for past, present and future - I'm lost.
And don't get me started on rings around Uranus!

Hilary Melton-Butcher said...

Hi Bazza - I'd hoped to have time to look at his documentary - hopefully it'll be shown again sometime ... it does sound so interesting ... cheers Hilary