Subject

[Glenn]

"When the universe began, it was filled with light which then travelled through the cosmos. And, if the universe began 13.7 billion years ago and we’re just now seeing it arrive, it had to have traveled 13.7 billion light years before it hit Earth."

https://www.youtube.com/watch?v=vIJTwYOZrGU

Reading more, it seems this guy really thinks the Earth existed in "the cosmos" when the universe began, with light from the Big Bang taking 14 billion light years to reach the Earth. Nah, can't be.

[Robert Carnegie]

Generally I favour "reading more", but I don't know what
you mean here.

Light existed after the Big Bang, but it wasn't going anywhere
for the first 300,000 years or so. That's the age of the
"cosmic microwave background" radiation.

But if you say, "it traveled 13.7 billion years before it hit
the astronomer Carl Sagan", that does not imply that the
astronomer Carl Sagan is 13.7 billion years old.

I think you have misunderstood.

[RonO]

My guess is that you are misinterpreting what he is claiming. There is
light from over 10 billion years ago that we are just observing getting
here with equipment like the Hubble telescope. NASA claims that the
Hubble has detected a galaxy 13.4 billion light years away. Our galaxy
may not have existed when this light first began it's journey, but this
region of the universe would spawn our galaxy and the star cluster that
contains our solar system. Our star would not have existed back then.
It would take over 8 billion years for the elements that make up our
solar system to be created. This doesn't mean that the light hasn't
been traveling for 13.4 billion years. We just happen to be here to
detect it as it passes.

Ron Okimoto

[jillery]

You think correctly. I thought of a few pedantic objections to the
video. Your comment about distinguishing light before and after the
CMBR is one of them. The video could have been more clear about that.
But in the main, its explanation is a good one IMO for the meaning of
the observable universe.

The video explicitly describes Glenn's quotemine as a superficial
understanding of how light behaves. The expansion of spacetime adds
to the distance light had to travel since the beginning of the
universe. What makes it even more complicated is that the expansion
speed has changed over time.

--
You're entitled to your own opinions.
You're not entitled to your own facts.