You are here:

Physics/Timeline of our cosmos


How did the material to make earth get here before the light of the deepest galaxies did??  I've tried to draw a map timeline, even from different perspectives and locations of each and I can't get the math to work out. I realize some light is way past us..but to me that means the big bang MUST be a looong process

Your question betrays a common misconception about the Big Bang -- one not helped by numerous popular presentations on the topic.

Contrary to popular belief, the Big Bang was NOT an explosion of matter from a central point into empty space. Rather, it was an EXPANSION of SPACE ITSELF.
Matter is NOT flying away from a spot in our Universe about 13.7 billion light years distant. Rather, space itself is expanding, and (more or less) matter is standing still. The distance between galaxies is increasing, but NOT because they are flying away from each other -- it's because the space between galaxies is growing larger.

I'm fully aware that the above paragraph is difficult to understand, simply because it was difficult for ME to understand. The BEST analogy I found was this:

Imagine the space in our Universe as a balloon, and matter is like ink spots on that balloon. The WRONG idea about the Big Bang is that it is like a spattering of ink, spreading out from the point where the pen dropped ink on the balloon. The BETTER idea is that the Big Bang is like a balloon expanding its diameter, with the ink spots growing further and further apart because the balloon (ie, "space") is growing larger. Note that, in this analogy, all parts of the balloon are equal -- none of them can claim to be the "center" or the starting point of the expansion.

Note also that this analogy is incomplete because (1) the surface of the balloon is two-dimensional, while the space in our Universe is three-dimensional; (2) the balloon has a center and is expanding INTO something (the air around it), while our Universe is just expanding; and (3) the balloon is curved, while space in our Universe (as best we can determine) is "flat" (I know it's hard to imagine a 3-D object being "flat," but, in math, the term applies to both 2-D and 3-D objects).

Thus, the point in space 1 micron from your nose is just as much the center of our Universe as any other point. All had (ALMOST exactly) the same quark density within .000001 of a second after the Big Bang; and all points had (about) the same photon density when recombination occurred.
The photons that broke free during that event eventually became the cosmic microwave background radiation (CMBR) -- the radiation I presume you are referring to as "light." Since these photons broke free at all points in our Universe, every point in our Universe is now getting CMBR from all directions, and will continue to do so forever. Think of the CMBR as like spam, only it's the same message, from all directions, and it has (and will) continued for tens of billions of years.

About half a billion years after recombination, the hydrogen and helium atoms that were finally able to be formed began to cluster and coalesce into stars and galaxies; one such cluster eventually forming our Milky Way Galaxy. Once again, all points in our Universe are equally a source AND a receptor of the CMBR; this includes the outer limits of the Milky Way where we happen to reside. The mass, that eventually became us, was there all the time -- it didn't have to travel any distance at all. The CMBR photons took 13.7 billion years to reach us, and those that were formed at a SLIGHTLY greater distance will continue to arrive.


All Answers

Answers by Expert:

Ask Experts




I can help with understanding physics that does not involve eggs. I will NOT help with academic or professional questions, which are NOT limited only to homework. Please do not waste your time by asking a question that comes out of ANY kind of academic, professional, or business matters.


Have been fascinated by physical laws ever since I learned, at age seven, that magnets work under water. My study continued through college and has not ceased even after I retired.

B.A. in Physics (with honors) from University of California at Berkeley.M.A. in Physics (with honors) from University of Texas Austin.

©2016 All rights reserved.