What is the difference between homogeneity and isotropy?
This is a question more of semantics than cosmology. It is said that our universe is "homogeneous and isotropic" (on large enough scales). Doesn't the word 'homogeneous' imply or include 'isotropic' by default?
Neither word implies the other must be true; it is possible to have something that is homogeneous but not isotropic (eg. equally spaced stripes which definately have a prefered direction) and it is also possible to have something isotropic but not homogeneous (eg. concentric rings which look very different depending on where you are, but are isotropic if you are in the middle).
Get More 'Curious?' with Our New PODCAST:
- Podcast? Subscribe? Tell me about the Ask an Astronomer Podcast
- Subscribe to our Podcast | Listen to our current Episode
- Cool! But I can't now. Send me a quick reminder now for later.
- Could our position in the universe affect our perceptions of the expansion?
- Why do we assume that the universe is homogeneous?
- What do "homogeneity" and "isotropy" mean?
How to ask a question:
If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.
This page has been accessed 22289 times since April 30, 2002.
Last modified: May 1, 2002 12:00:00 AM
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.
Warning: Your browser is misbehaving! This page might look ugly. (Details)