Expert: James Gort - 5/28/2007

Question
QUESTION: Hi,

In a recent lecture it was stated that the observable universe is fourteen billion years old, but forty-plus- billion light years "wide."

How did it get so big in so "short" a time?

I realize that space can expand--and has expanded--faster than the speed of light. But, even if this is the case, I would think that light, which is limited to, um, the speed of light would not have had time to reach us to be observed.

Even if we think of the observable universe as a sphere, so that it would be twenty-eight-billion light years "wide", this would still not give light from forty-billion-plus light years away to reach us.

As you can see, there's clearly something I'm missing.

Any help greatly appreciated.

Steve
nighttrain@nyc.rr.com

ANSWER: Hi Steve,

I wish I had attended that lecture!

First, let me say that this is a highly speculative area, and no one has "all" the answers.  Many times, ideas are based on not-very-well founded theories.  And there is no universally accepted theory in cosmology - there is considerable disagreement among scientists.  So don't believe everything you read (or hear in a lecture)!

That said, I honestly don't understand what is meant by "40 billion light years wide".  The universe is non-Euclidean, meaning we can't measure it with "straight" lines.  Light rays are curved, so that it could mean the distance light would have to travel to completely wrap around on itself.  In other words, with a strong telescope, we could look out in one direction, and if we wait 40 billion years, we could actually see the back of our heads!

In reality, we can see only about 10 billion light years away, where galaxies are receding at more than 50% the speed of light.  As we push the distance further, the recession velocity gets higher, so we could never see the "beginning".  It is thought that about 12 billion light years is the limit at which we can observe - light simply "disappears" as it gets red-shifted to the extreme.

But I caution you not to think of the universe as a sphere - unless you can visualize a sphere in 4 dimensions, warped by gravitational influences.  

I suggest the following book.  Written by three eminent cosmologists, it's also very readable.  That book (available from amzon.com or elsewhere) is:      

A Different Approach to Cosmology: From a Static Universe through the Big Bang towards Reality by F. Hoyle, G. Burbidge, and J. V. Narlikar.

That one book will answer most of your questions, and explain that there are many conflicting theories!

Hope that helps.

Prof. James Gort

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

QUESTION: Many thanks. Very helpful. I'll get the book.

Steve  

Answer
Hi Steve,

You're welcome.

If you still have a few dolars left, I also recommend "Seeing Red" by Halton Arp, another very respected astronomer, who insists that galaxies' red shifts have other explanations than just distance - and he describes them in detail.  In particular, he describes how the "accepted" velocity-distance relationship can't be correct.

Cheers,

Prof. James Gort