Thursday, August 6, 2009
Redshift Z In The Wild
Redshift z is used in astronomy to determine how far away an object is. The more the light from that object shifts to red, the farther away it is. Wikipedia has a good description of redshift.
While surfing NASA's site, I decided to record the redshift z and distance of objects when they were provided in the description. The distances of these objects ranged from 250 million light years away to 12 billion light years away.
What I found was rather surprising. The data don't seem to correlate very well. The redshift z doesn't seem to have an algorithmic relationship to distance.
You can see this for yourself in the charts above. The first chart shows redshift z as a blue line overlaying green distance bars. The two curves don't match up! The next two charts divide distance by redshift z and redshift z by distance. These two charts highlight that there is no smooth curve relating the values of redshift z and distance.
I also tried normalizing the redshift z and distance values to a scale of 0 to 1. This didn't change the results, as you can see in the image below.
I don't know if these numbers simply represent errors in the values provided on NASA's website, if there's something I'm misunderstanding, or if the redshift z theory really uses these unusual values. I think I'll shoot an e-mail to NASA and try to get an explanation.
Here is what the relationship between redshift z and distance looks like in theory. You can see how smooth the curve is in theory. Not at all what the curve looks like in practice.
Redshift z values are multiplied by 10,000 in the charts I provided. This was done so they'd be on a similar scale to distance values, otherwise you wouldn't be able to see them in the charts that had scales large enough to show distances. Scaling the redshift z values in this way does not affect the results I discuss here.
Data (Late Edit: By request, chart modified to include object names)
Wikipedia Cosmology Distance Measures