Cosmological principle Definition and 24 Threads

In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale, since the forces are expected to act uniformly throughout the universe, and should, therefore, produce no observable irregularities in the large-scale structuring over the course of evolution of the matter field that was initially laid down by the Big Bang.

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  1. M

    I Expansion of the Universe and the cosmological principle

    Wikipedia states the following in their article about the expansion of the universe: If the cosmological principle was discovered to be false in our universe, i.e. our universe was discovered to be inhomogeneous or anisotropic or both on very large scales and the FLRW metric does not hold for...
  2. elcaro

    I Cosmological principle about space and time

    AFAIK there is no cosmological principle formulated about space and time. If it would be formulated, it would more or less state that spacetime is an interconnected whole, and has no gaps, edges or boundaries. It doesn't need to state wether spacetime is finite or infinite, that is an open...
  3. S

    I Does the CMB reference frame violate the Cosmological Principle?

    Studies of the Cosmic Microwave Background shows that the Earth is moving roughly 380 km/s with respect to it towards the constellation Leo I think. Yet (I think) the Cosmological Principle and the Michelson-Morely experiments suggest there is no preferred reference frame in the universe --...
  4. C

    A The Cosmological Principle means infinite Observable Universes

    I am posting to ask for any comments about a couple things. I will post a link to a thread on another forum about this. and would love to hear any and all thoughts about it. the thread begins asking about 2 things. the first one is about how fast we are moving. I,402,00 mph relative to the CMB...
  5. G

    I The Cosmological Principle and the Universe

    The cosmological principle seems to hold well, and would imply an infinite amount of matter in the universe if the universe is flat and unbounded
  6. Arman777

    Insights A Journey Into the Cosmos - The Friedmann Equation - Comments

    Greg Bernhardt submitted a new PF Insights post A Journey Into the Cosmos - The Friedmann Equation Continue reading the Original PF Insights Post.
  7. C

    B Shape of Universe & Cosmological Principle

    Let me preface this post by saying that I only have a very cursory understanding of general relativity. I happen to know that if we assume the cosmological principle, then the hypersurface ##\Sigma_t## of the spacetime manifold ##M##, for any positive ##t##, is either a 3-sphere, a...
  8. R

    Some questions on the Cosmological Principle

    Firstly, I am just a very interested layman so please forgive my ignorance and non mathematical approach. As I understand it, the cosmological principle states that on larger scales the universe is homogeneous and isotropic. So could someone help me to understand the following: 1) Does this...
  9. yazanhomsi

    Who First Conceived the Idea of the Cosmological Principle?

    Good day all, A question that I haven't really found the answer for yet: "Whom did first come up with the idea of the cosmological principle?" I almost looked everywhere for the answer but still cannot find it. Was it Friedmann or Lemaitre? Or was it some other great physicist? But there...
  10. A

    Is the CMB Data Showing that We are the Center of the Universe?

    Two days ago, I have opened theme about fine-tuning on which I got good answers... Now, there is another topic, on which I have question... The reason why I am asking this question here, is because I want to get correct answer... Internet is full of trash and misinformation, and this is a...
  11. andrewkirk

    A Cosmological Principle: Trying to define large-scale homogeneity

    I have been trying to pin down a precise definition of large-scale homogeneity, in the context of saying, per the Cosmological Principle, that all constant-time hypersurfaces (CTHs) of a foliation are large-scale homogeneous. Here is my attempt: Let M represent any coordinate-independent...
  12. J

    Perfect cosmological principle in co-moving co-ordinates

    To quote cosmologist Ned Wright: If the Universe is the same at all times, it is argued that the value of the Hubble parameter must be a constant H_0, so H = \frac{\dot{a}}{a} = H_0 leading to an exponential cosmology a(t) = e^{H_0 (t - t_0)} where t_0 is the present age of the Universe...
  13. H

    Revamping general concept and cosmological principle

    Why would we assume matter is spread homogeneously throughout the universe if its only 4.6% of universe :confused: The universe is believed to be mostly composed of dark energy and dark matter, both of which are poorly understood at present. BBT explains about CMBR, redshift, expansion and...
  14. TrickyDicky

    Cosmological principle and quasar distribution

    Our cosmology model follows the cosmological principle according to which we are not in a privileged place in the universe and there is homogeneity, but if you take a look at the distribution of quasars in the universe there seems to be a "quasar spherical void" roughly one billion lightyears...
  15. tom.stoer

    Questioning the cosmological principle

    The cosmological principle essentially says that there are no preferred locations and directions in the universe (homogenity and isotropy). We know that strictly speaking this principle is violated at the accessible scales (filaments, galaxy clusters and supercluster, voids, CMB). So one could...
  16. A

    Is the Cosmological Principle Limited to Space Only?

    The cosmological principled as applied to modern cosmology and the standard model concerns only the spatial part of spacetime, this has been criticized based on Minkowski's predicated non-separability of spacetime, that led(among other things) to the "perfect cosmological principle" that...
  17. S

    Is the Cosmological Principle a Product of Our Perceptions or a Universal Truth?

    How do we know that the universe is isotropic and homogeneous and why do we succumb to accepting that there is no special place in the universe that is the center? Since if everything is expanding from everywhere else at the same rate, there is still going to be a point center where everything...
  18. H

    Mathamatical Description of the Cosmological Principle

    I think this belongs here, while not relativistic, is is about objects moving relative to one another. Summery: This stems from the description of 'Dark Energy' in a mathamatical context to show that you can place a 'center of the universe' at any point in space, and the accelaration vector...
  19. K

    Ray of light travelling through universe (applying cosmological principle)

    cosmological principle states that, on large spatial scales, universe is homogeneous and isotropic. in other words, universe looks the same in every direction and that is true for every point of view. there are some challanges to this principle, but for this discussion, I will assume it is...
  20. Q

    Is the Hyperboloid Model Truly Homogeneous and Isotropic?

    Hi: The principle states that : the universe is homogeneous and isotropic. Then we have three solutions often depicted as i) Sphere ii) Plane iii) Hyperboloid I can understand that the sphere and plane is homogeneous and isotropic, but the iii) does not seems to be. There seems to be a...
  21. MathematicalPhysicist

    Theories without the use of cosmological principle.

    are there theories in cosmology which do not incorporate/use the cosmological principle?
  22. E

    The cosmological principle in simple models of the universe

    NOTE: Taken from another thread on a similar subject: https://www.physicsforums.com/showthread.php?t=125698 "An infinite amount of space with matter uniformly distributed throughout", is not a claim of infinite matter – at least it shouldn't be. If matter is assumed to be inside of a greater...
  23. M

    Bad Science and the Anthropic Cosmological Principle

    "Bad Science" and the Anthropic Cosmological Principle Many observers have noted that the physical laws, parameters and constants of our cosmos appear to be remarkably "fine tuned" in accordance with our existence. There are a number of suggestions that if certain parameters were to be...
  24. T

    Cosmological Principle: Finite or Finiteless Universe?

    The Cosmological Principle says that the universe is homogenous and isotropic. Doesn't this imply that our universe cannot be in finite size, but is finiteless? If it has a boundary, how can then the cosmological principle still be true for those heavenly bodies residing at the boundary of the...
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