Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Alan McDougall on 28/05/2016 01:47:32

Title: How can we still see the light of ancient quasars?
Post by: Alan McDougall on 28/05/2016 01:47:32

When astronomers look into the depths of the universe , they find the light of quasars that left them billions of years ago with a huge red-shift.

They tell us that in this that they are looking back at the universe when it was still young, when in fact they are looking at the light from some of the most ancient objects in the universe.

What baffles me, is how can we on our 5 billion year old planet, are still picking up photons on our telescopes, from objects that came into existence almost 13 billion years ago and most likely have left the universe as we know it?

As the photons left the quasar, it receded at almost c, something like a base ball player throwing a ball, while at the same time running in the opposite direction.

Am I correct in my understanding?

Alan

Title: Re: How can we still see the light of ancient quasars?
Post by: PmbPhy on 28/05/2016 05:46:46

Quote from: Alan McDougall on 28/05/2016 01:47:32

When astronomers look into the depths of the universe , they find the light of quasars that left them billions of years ago with a huge red-shift.

They tell us that in this that they are looking back at the universe when it was still young, when in fact they are looking at the light from some of the most ancient objects in the universe.

What baffles me, is how can we on our 5 billion year old planet, are still picking up photons on our telescopes, from objects that came into existence almost 13 billion years ago and most likely have left the universe as we know it?

As the photons left the quasar, it receded at almost c, something like a base ball player throwing a ball, while at the same time running in the opposite direction.

Am I correct in my understanding?

Alan

Yes. You're correct. Just because the light is redshifted it doesn't mean that it can't be detected by us. All that means is that the light spectrum of the quasar is shifted towards the red.

Title: Re: How can we still see the light of ancient quasars?
Post by: evan_au on 28/05/2016 13:12:40

Quote from: Alan McDougall

how can we on our 5 billion year old planet, are still picking up photons on our telescopes, from objects that came into existence almost 13 billion years ago

It's because the travel time is almost 13 billion years.

They were emitted almost 13 billion years ago, they travelled for almost 13 billion years, and we detect them today.