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Fraser
2004-Sep-15, 04:33 PM
SUMMARY: It will probe the dark ages before the era of re-ionization, and perhaps before the birth of the first stars. It will observe the formation of the first galaxies. It will map the web of neutral Hydrogen that is spread across our universe, near and far. In 2015, an array of 4400 twelve meter fully steerable paraboloid radio dishes, called the Square Kilometer Array (SKA) is scheduled to be complete and operational.

What do you think about this story? Post your comments below.

Pedantic
2004-Sep-15, 07:44 PM
:blink: HI folks:

This is a question that has plagued my mind for a while, and the story about the square kilometer array allows me to get it off of my chest.

Now, please do not misunderstand me. I believe the universe is between eight and fifteen billion years old; I do not doubt that assertion one bit, but I fail to see how us looking at light fifteen billion light years away (or whatever) can be assumed to be the beginning of the universe--my doubts are based upon geometry, and the assumption that the speed of light solidified at a fairly young age for the universe. Please look at the following highly inadequate drawing of the expansion of the universe:

PL----------------PP----------------B----------------PP----------------PL

Assume that B is the location of the big bang. PP is our current location (Position of planet). PL is the location of the radiation thrown off from the big bang, in general terms. From that massive explosion the universe begins expanding outward in a fairly uniform way (shouldn't it?). Because electromagnetic radiation travels faster than solid matter in just about any case that I can think of, though the solid stuff and the light stuff (please assume the labels as clumsy metaphors) started off at the same time and location, the light stuff from that period in the universe should be well beyond our ability to observe, regardless of which direction we look. So how can scientists claim that what we are seeing fifteen billion lightyears away is from that period? If one looks at the geometry of the situation, it just doesn't add up, unless, of course, I'm missing something.

What if our universe has had several cosmeggs and what we are seeing is not the origin of our cosmegg, but of another in a distant part of the universe? Anyone who has read Brian Greene's "The Elegant Universe' may understand how that might be possible.

Anyway, this question has troubled me for quite a while. I have asked it in other forums, and I usually get some kind of brush off. How about you guys giving it a try?


TIA! :)

antoniseb
2004-Sep-16, 12:24 AM
Originally posted by Pedantic@Sep 15 2004, 07:44 PM
PL----------------PP----------------B----------------PP----------------PL
You can't really look at it that way you have diagrammed it. That being said, it may be useful for you to imagine that what we are seeing, and calling light emitted from shortly after the big bang [however long ago it was - current best guess 13.7 Gyears] is that we are looking at things on the other side of the 'B' in your diagram when we do that. The 'B' is somewhere around z=1.

Tim Thompson
2004-Sep-16, 04:29 PM
Pedantic: ... but I fail to see how us looking at light fifteen billion light years away (or whatever) can be assumed to be the beginning of the universe ...

That's easy. You are correct, it isn't the beginning of the universe.

I didn't see the news story, so I don't know what it said. But I do know that new stories are notoriously incomplete, often misleadingly simplistic, and more often than we wish, they are just plain wrong. So if you got that idea from news stories, don't feel lonely.

We can only use electromagnetic radiation (http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html) to see the universe when it was about 300,000 years old & older. Prior to that, the universe is opaque to electromagnetic radiation (radio, light, & etc.), and something else must be used to see deeper into the past (cosmological relic neutrinos (http://www.cerncourier.com/main/article/39/2/14) and gravitaional waves (http://astron.berkeley.edu/~elevine/node8.html) should both do the job of probing all they way back to perhaps a second or less, after the Bang).

The Square Kilometer Array (http://www.skatelescope.org/) is so named because the collecting area of the combined telescopes will be one square kilometer, far greater then any other radio telescope(s). The large collecting area means increased sensitivity, just like getting an amateur telescope with a bigger mirror. That means it can detect weaker radio emissions than any other telescope, and it can measure polarization as well. By looking at the universe with such an instrument, we see the baby universe, but it has imprinted on it, physical signatures of the events which happened in the electromagnetically invisible past. We can compare those observed signatures with theoretical predictions, and thereby enhance our understanding of the physical history of the as-yet invisible past (with some speculation obviously involved).
Collected pre-prints of technical papers on the Square Kilometer Array (http://arxiv.org/find/astro-ph/1/abs:+AND+array+AND+square+kilometer/0/1/0/all/0/1)

StarLab
2004-Sep-16, 04:37 PM
PL----------------PP----------------B----------------PP----------------PL

Assume that B is the location of the big bang. PP is our current location (Position of planet). PL is the location of the radiation thrown off from the big bang, in general terms. Of course, Pedantic, you are missing something highly relevant to recent decade's thinking, partiularly from the mind of Stephen Hawking...your diagram should instead look like the following:

B----------------PL-----------------PP----------------PL----------------B

So you see, this fits the idea that we are looking out 'into' the past.

StarLab
2004-Sep-16, 04:39 PM
Remember, Pedantic, what Einstein said: space-time.

(Q)
2004-Sep-16, 05:11 PM
PL----------------PP----------------B----------------PP----------------PL

'B' and 'PP' will always be comprised of the same coordinates as will 'B' and 'PL'. So, essentially the view is PP relative to PL, B is not required.

StarLab
2004-Sep-17, 02:46 AM
For the sake of time, yes, it is. :(