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Name: Mark
Status: other
Grade: other
Location: NV
Country: N/A
Date: N/A


Question:
Where the universe is expanding on the edge right now, is about 13.8 billion light years away. Relative to the earth, is this edge older or younger than the Big Bang? If I had to guess I would say it is older? Because it is expanding away from us. If this is true please explain to us how it could be that where the edge of the universe is and stars do not even exist yet, is the oldest and newest part of the universe at the same time? (I hope you know what I am trying to ask? Please rewrite if it if is unclear.)


Replies:
Mark,

If we imagine the Big Bang to be the birth of the universe, then we can not imagine that any light source would be younger than that event. Suppose now that light from a distant object leaves that object and heads toward us. This light contains information about that object at the time the light left that object. Now the light travels to us and takes 13 billion years to get to us. So now, when we receive the light, we are receiving light that contains information about the object *when it left* 13 billion years ago. This does not mean that the object far away is 13 billion years younger, it will have age in the intervening time, it just means that the information we receive is 13 billion years old and we are obtaining information from 13 billion years ago. The farther an object is, the longer the light gets to us, and the older the information is.

Greg (Roberto Gregorius)


The number you refer to, 13.8 billion years refers to the AGE of the Universe, not its "size", it has no edge, in the sense that there is something "out there" on the other side of some boundary of the Universe. See:

http://www.astro.ucla.edu/~wright/age.html.

Now there are two problems. The first is that the age of the Universe is "model dependent", that is it varies depending upon what experimental criteria you use to set the standard. This is discussed in the web site above. The age determined by the various models vary from 11 to 17 billion years, but tend to "cluster" around 13 to 14 billion years. There is yet another problem "in principle", and that is the finite speed of light. The speed of light is about 3x10^5 km, there are about 3.16x10^7 seconds in a year, and if we take the age of the Universe to be 13.7x10^9 and multiply these together you find that frontier of the Universe that we are able to observe is about 1.3x10^23 km. The "light" from any object further away than that has not had enough time to reach us yet.

So the Universe could be larger than we are able to observe.

Vince Calder



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