Is the Universe Homogeneous or Isotropic?

In summary: The comoving coordinate system was first used in the early 1940s to study the large-scale structure of the universe. It is still useful for examining the structure of the universe on a large scale.
  • #1
biggiekjac
6
0
I recently read an article about whether the http://dailyphysics.com/" [Broken] and/or isotropic. (the story is at the top - sorry I couldn't get the link to the permanent article to work here) “gargantuan ripples in the density of matter across the universe, known as baryon acoustic oscillations” is what the article says causes inhomogeneities in the universe, and that we can test for them.

First of all, do you think the universe is homogeneous and/or isotropic? Why or why not?

and

Second, how would we be able to realistically test these properties? Would we have to send a spaceship to the far reaches of the universe and measure the force of gravity between some set of standardized masses? Thoughts on this?
 
Last edited by a moderator:
Space news on Phys.org
  • #2
This one?

http://adsabs.harvard.edu/abs/2008arXiv0810.4939G

As an alternative explanation of the dimming of distant supernovae it has recently been advocated that we live in a special place in the Universe near the centre of a large spherical void described by a Lemaitre-Tolman-Bondi (LTB) metric. In this scenario, the Universe is no longer homogeneous and isotropic, and the apparent late time acceleration is actually a consequence of spatial gradients. We propose in this paper a new observable, the normalized cosmic shear, written in terms of directly observable quantities, and calculable in arbitrary inhomogeneous cosmologies. This will allow future surveys to determine whether we live in a homogeneous universe or not. In this paper we also update our previous observational constraints from geometrical measures of the background cosmology. We include the Union Supernovae data set of 307 Type Ia supernovae, the CMB acoustic scale and the first measurement of the radial baryon acoustic oscillation scale. Even though the new data sets are significantly more constraining, LTB models -- albeit with slightly larger voids -- are still in excellent agreement with observations, at chi^2/d.o.f. = 307.7/(310-4)=1.005. Together with the paper we also publish the updated easyLTB code used for calculating the models and for comparing them to the observations.
 
  • #3
biggiekjac said:
First of all, do you think the universe is homogeneous and/or isotropic? Why or why not?

Isotropic, homogeneous Friedmann-Robertson-Walker models seem to model observations well on very large cosmological scales.
Second, how would we be able to realistically test these properties? Would we have to send a spaceship to the far reaches of the universe and measure the force of gravity between some set of standardized masses? Thoughts on this?

See

https://www.physicsforums.com/showthread.php?t=250204.
 
  • #4
Yeah that's the one, thanks.

Jim Graber's link in that thread, George, to the animation of the formation of the acoustic peak is good. I'm not familiar with the comoving coordinate system that the page references, though. Does anyone know when this comoving coordinate system was first used? Is it only useful for examining the structure of the universe on a large scale?
 

1. What does it mean for the Universe to be homogeneous?

Homogeneity refers to the idea that the Universe looks the same at every point in space. This means that on a large scale, the distribution of matter and energy is uniform and does not vary significantly from one point to another.

2. How is homogeneity different from isotropy?

Isotropy refers to the idea that the Universe looks the same in all directions. This means that there is no preferred direction in the Universe, and the laws of physics are the same in all directions.

3. How do we determine if the Universe is homogeneous or isotropic?

Scientists use various observations and measurements, such as the cosmic microwave background radiation and the large-scale distribution of galaxies, to determine the homogeneity and isotropy of the Universe. These observations suggest that the Universe is both homogeneous and isotropic on a large scale.

4. Are there any theories that suggest the Universe is not homogeneous or isotropic?

There are some theories, such as the fractal cosmology theory, that suggest the Universe may not be completely homogeneous and isotropic on all scales. However, these theories are still under debate and have not been widely accepted by the scientific community.

5. What implications does the homogeneity and isotropy of the Universe have on our understanding of the Universe?

The homogeneity and isotropy of the Universe are important principles in our understanding of the Universe, as they provide the foundation for the cosmological principle - the idea that the laws of physics are the same everywhere in the Universe. This helps us to develop models and theories to explain the origin and evolution of the Universe.

Similar threads

Replies
27
Views
4K
  • Cosmology
Replies
11
Views
2K
  • Cosmology
Replies
8
Views
2K
Replies
1
Views
1K
  • Beyond the Standard Models
Replies
20
Views
2K
Replies
29
Views
2K
Replies
9
Views
1K
  • Cosmology
Replies
4
Views
3K
Replies
86
Views
15K
Back
Top