Expert: Tom Whiting - 10/30/2004

Question
Hello and thanks in advance,

The recent "Hubble Ultra Deep Field" - (HUDF) showed some smudges believed to be galaxies at a distance (according to Hubble's law) of 13.8BLY. It was claimed that this was seeing to within a few percent of the time of the Big Bang.


For this question I will use 14BLY and assume the number is reasonably close, and either the center of our galaxy or the point in space/time where the photon was detected as the center of the reference frame.

The other assumptions are that the object was 14BLY away - having taken more than 14BY to get that far away from us( at less than the speed of light) - at a time of 14BYA; when it emited a photon (quite beautiful, actually) that was recently detected by our telescope - after  traveling at the speed of light for 14BY.

If I'm not mistaken, there is no requirement for the universe to be homogenous and isotropic, it would just make the math easier.

(Personally, I claim that the universe is MORE homogenous and isotropic at larger scales...)



ANYWAY...

 Wouldn't a galaxy (photon emitter)take as long or longer to get to a point - when and where it emits a photon we detect - than it takes for that photon to get from that point to here?

 Wouldn't a "perfect" telescope actually be able to only see 1/2 (one half) way to the time of the big bang?"




Thanks for your time,

Donald Barger Jr.

dbargerjr@yahoo.com
geocities.com/dbargerjr/page1.htm
208-852-7177

9862 N Hwy 34
Preston, Idaho 83263-5074  

Answer
Hi Don....
Sorry, but I never received your question from the Allexperts
group; I typically answer within hours of a question....
But, here we go....
Ahh...the photon we receive at what we perceive a distance today of, say 13.8 BLy, was not emitted at that distance;  it was emitted probably more like when the galaxy was at the 13.4 BLy distance, and has presently moved to the greater distance, during the travel time,  using OUR reference frame.

 Remember, a clock aboard those incoming photons at light speed, would show zero time elapsed during their light speed travel, in their reference frame....in fact, EVERY photon
zipping around the Universe feels that it just immediately
left its source, no matter how much of our "Earth-timeframe" time has elapsed.

OR, to put it another way,
at the current 14 BLy distance (a photon emitted tonight) won't arrive here for 14 Billion years (our Earth years), by which time that distant galaxy will have probably moved (due to the accelerating expansion of space) to 15 or 16 BLyears
distant.  All this has to be factored in when we consider
the distance to those early galaxies.  That's why its
easier, and perhaps more accurate,  to express not the distance, but rather the time factor, a percentage relative to the Big Bang creation scenerio.  


As far as homogenity,  perhaps right after the BB the
Universe was very homogenous, but the only way to
form up clumps of matter is to have gatherings of material
and this involves slight temperature variations in the
after-glow of the BB, which the spacecraft COBE of the
early 1990's showed to be true.  Thus accounting for the
"spiderweb" appearance of the Galaxy Clusters and the
huge, nearly empty,  voids we see throughout the Universe
on the very large scale.

Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA

FOLLOW -UP:
Opps...didn't see the rest of your question....

Well, I don't think the calculations imply that the
region of space immediately surrounding the BB
region is traveling away from us (or us from it)
at near-light speed.....so no, a telescope is actually
seeing the light of within a few percent of the
age of the Universe.  Distance-wise, it may be
actually farther away, but again, that's why its
more accurate to say, Well, we are looking at
a galaxy that formed within 5% of the total age
of the Universe.
Clear Skies,
Tom Whiting
Erie, PA

Oh, please visit our club website for great picts
of my new 30 inch portable truss DOB scope...
at
http://www.velocity.net/~bwhiting/