Expert: Ed - 5/22/2009

Question
QUESTION: I guess I must be missing something obvious, but I've had this on my mind for a long time and can't see the error in my thinking.

Light travels at a fast, but finite speed, so we see things not as they are now, but as they were when the light left the object.
If follows from that, that the further an object is away, the further back in time we're looking at it.
So far, so good.

But we often hear astonomers talking about seeing back ever close to the origin of the universe - to the big bang.
And this is what bothers me. Please fault me reasoning for me:

Any event only happens once - and the instant and the instance of that event is never repeated.
An "event ripple" propogates outwards from that event at light speed, but if you miss that event - if it passes you before you started looking - you'll NEVER SEE IT.
So, for example, consider the the sun, which is 8 light minutes from Earth.
If it exploded NOW, and you slept for the next NINE minutes - you'd miss it forever (of course, you'd be dead so the point is practically moot).

Now unless the universe expanded faster than light speed for some of its history, the "event ripple" of the Big Bang will always be beyond anything in the universe, and so no one/thing will ever see it - and no one/thing ever did. In fact, it defines the limits of the universe - and if you're in it - you can't see it.

Where did I go wrong?

Thanks,
Chris

ANSWER: Chris, this is very interesting stuff.  I will share some of my thoughts.  Please get back to me if you would like to talk about this more.  This weekend is a long (holiday!) weekend in the United States, so I will have more time for things like this.

Okay, first of all, please look at this NASA website:
http://map.gsfc.nasa.gov/universe/bb_tests_cmb.html

On that website, scroll down to the section entitled "The Origin of the Cosmic Microwave Background."  Start reading the paragraph which begins "Since the universe was so very hot through most of its early history," and read all the way to the end of the webpage.

The idea is that the radiation from very early in the universe, (whether it was visible light, microwave radiation, or whatever), travelled in ALL directions very early in the history of the universe.  This means that it travelled INWARD as well as OUTWARD.  So the "event ripple" from every point in the early universe is still travelling in ALL directions, not just at the extreme outer edge of the universe, as you describe.

I think that should basically answer your question.  This topic is complicated.  I hope you get back to me in a few days, because I want to study this some more so I can tell you more.

Keep Looking Up,
-Ed

---------- FOLLOW-UP ----------

QUESTION: Hello Ed and thanks for making time to help me out.

I read the article extract you referenced, and your
comments, but I'm sorry to say that I am none the wiser.

I understand that the early universe radiation travelled in
all directions, but I don't see how that fact removes the
issue I have with "looking back to the big bang".

In the beginning, the universe was a singularity, and in
that context, it's difficult to find a meaning for the word
"inward", because there were no spacial dimensions of non-
zero length.

Nor can I get a hold of what you mean when you say the
primordial event ripple is still travelling in all
directions.

Certainly an event ripple is spherical and so it expands to
visit all points in all of space, eventually. But my point
was that it will only visit any particular point in space
ONCE, and the time it visits that point is a direct
function of the speed of light and that point's distance
from the cosmic origin. Furthermore, the current extent of
that ripple would seem to me to be the limit of space-time
itself, and so the only points in space which can currently
"see" the big bank are those points add the outer boundaryt
of the expanding universe.

I know I'm wrong, I just can't see why I'm wrong.

Want to have another crack? Anyone??

Thanks,
Chris

Answer
Chris, maybe somebody else has already helped you with this.  I just wanted to pass something along.  I still have trouble understanding this, so I don't think I can absolutely answer your question.  BUT I think this article will HELP, and maybe give you some more specific terms that you could google yourself.
http://en.wikipedia.org/wiki/Metric_expansion_of_space

I wish I understood this better.  I hope this is at least a little helpful.

Best,
-Ed