Are scientists missing the point with distant cosmic objects, or is it just me?

Question

I was reading this article this morning:

http://www.bbc.co.uk/news/science-environment-13539914

Scientists have discovered a gamma-ray burst whose light has taken 13.14 billion years to reach Earth. This much is cool and interesting. However, the assumption is then stated that this is "the most distant single object yet spied by a telescope".

But hold on a minute. It is also known that galaxies are moving away from each other at incredible speeds, most faster than the speed of light, because the space/time between them is expanding (or something like that... I'm no scientist!)

So these so-called amazingly distant objects, well for starters, they don't exist any more... They are things that happened billions of years ago. But not only that, they are probably objects that were only a few million light years away from us when they actually took place. So surely then, the objects themselves aren't the most distant ones, but the light from them has been distorted such that the light has taken that long to reach us?

Furthermore, if the galaxies are spreading out faster than the speed of light, who is to say this explosion actually happened 13.1 billion years ago? Isn't it possible that the light was created say 5 billion years ago, but has taken much longer to reach us because of the expanding space between the galaxies?

I'm sure this stuff has already been considered by scientists, but I find it weird the way news articles always assume that just because light travels at a specific speed, that it's always going to take the same amount of time to reach us.

Or am I getting it wrong? I'd love to know!

:-Joe :)

Answer 1

Looking at a distant object, billions of light years distant, has many connotations.

By being so incredibly far away, you're seeing past events. But this does not necessarily mean the object no longer exists. It may still be around, but certainly could be very different.

I recommend checking out some of the starter Astronomy videos like this one at Khan Academy, it helps me get a handle on the scale of things and the physics behind it.

Answer 2

Of course the expansion of space is being considered by astronomers. In fact, it's pretty much the only thing they are considering. The redshift due to expansion of space is the way that astronomers know that it came from 13.14 billion years ago. What you do is look at the lightwaves very carefully. They will be stretched out (which looks like redshifting) due to the expansion of the universe. The longer they have been flying along, the more stretched out/redshifted they will be. The group cited in the article measured a redshift (a measure of this stretching) of 9.4, which is the largest we've ever observed; we conclude that this light has been traveling longer than any other light we've observed from a single source (the cosmic background radiation is way more redshifted).

A number of very clever methods allow us to identify just how long the light must have been traveling for it to received a particular amounts of redshift. This is an application of the relation known as Hubble's Law. If you use it, you find that light with a redshift of 9.4 has been traveling for about 13.14 billion years.

This method is used so routinely that you'll hear cosmologists talk about time in terms of redshift, like "Ionization occurred at redshift 17" rather than "Ionization occured 13.5 billion years ago" (those numbers are made up).

Answer 3

One of the reasons why scientists like to took at distant objects is because they know that, by doing so, they're looking back in time: a distant object is an object from the past. A very distant object (like the one you cited) is an object from near the beginning of the universe (which is interesting to people who want to know about the beginning of the universe).