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What is the definition of cosmology in a physics context?

  1. Aug 12, 2013 #1
    "Cosmology is the scientific study of the properties of the universe as a whole."

    That definition seemed concise and straight to the point for both scientist and the public. Everything else cosmology contains seems would be included within that definition. Does anyone here have a better one sentence definition of cosmology at works for both scientist and the public?

    Thanks for your time to answer this simple question.
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  3. Aug 12, 2013 #2


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    I like Walter Isaacson's definition from his Einstein biography:

    "Cosmology is the study of the universe as a whole, including its size and shape, its history and destiny, from one end to the other, from the beginning to the end of time."

    A bit on the poetic side, but nonetheless accurate.
  4. Aug 12, 2013 #3


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    Hi Clayjay, I tend to be wary of what seem like prescriptive definitions. I know that for me the only workable definition of "Philosophy" is "what philosophers do".
    Same with mathematics. It is defined by a self-selecting community of experts and it really does change---it changes over the course of centuries as that cultural/traditional community evolves.

    So you can't TELL philosophers what they "ought" to be studying and doing in the name of Philosophy, by making some artificial definition that happens to sound good to you.

    I'm not sure what you mean by "properties". Is quantum mechanics a "property" of the universe?
    It seems to be pervasive, involving all matter, and possibly also geometry at high energy densities.
    So should Cosmologists be worrying about the foundations of quantum theory?

    Maybe they "should" but most of them don't at the present time in our history. It is not part of the job description.

    Basically what cosmology is about is the kind of mathematical modeling that will get you hired as a Cosmologist at a good university. Usually there is an astrophysics section of the Physics Department, that hires. Or there is a separate department of Astronomy/Astrophysics. It is whatever the hiring committee is looking for in your published work, if they have an opening for a Cosmologist.

    I'm not sure what you mean by "as a whole". Nowadays cosmologists are very interested in the processes by which galaxies form. But a single galaxy is an extremely small part of the observable universe. So should they stop being interested, and stop working on that?

    I guess the question I should be asking is what USE do you want the definition to serve?
    Definitions in normal human language are not true by some absolute standard, but they can be more useful or less useful.

    So you could tell me (or us) what you want to use the definition for, and I, for one, could try to judge how good the one you are proposing is for that purpose, or else propose an alternative.

    I think the main thing is, it's about large-scale GEOMETRY changing over time as it interacts with matter. We have this excellent equation of gravity called GR which is actually a dynamic equation of geometry itself (how geometry expands and contracts and bends over time as it interacts with matter).
    So the challenge for cosmologists is to USE that equation of how geometry evolves in order to construct a MODEL of the history of matter and geometry at large scale that they can TEST by fitting all the relevant observational data to. Some day if GR equation is ever replaced by a more advanced fundamental equation of dynamic geometry, then cosmologists job description will change and their challenge will be to build a model based on THAT NEW equation, whatever it is. And the model will be expected to fit the data even better.
    I'm afraid I may be telling you this very basic stuff that you already know. But maybe it needs to be said.

    Also what cosmology is tends to be OBSERVATION DRIVEN. If you add a new instrument to the mix, and make new observations, some cosmologist is likely to discover a puzzle or a question to ask and start to work on it. So detecting polarization in background radiation, or taking images of proto-galaxy blobs forming in early universe, or detecting an odd thing in the spectrum of high energy cosmic rays, or something peculiar about neutrinos could get a cosmologist's attention and start a new line of investigation. It's hard to predict (on basis of abstract generalities) just what cosmology is going to be about, say, ten years from now.

    It's about being curious monkeys in a big place. :biggrin:
    Last edited: Aug 12, 2013
  5. Aug 15, 2013 #4
    Thank you, the term "properties" is vague and unneeded.
    "Cosmology is the scientific study of the universe as a whole" seems more concise to me now. Or, maybe "Cosmology is the scientific study of the entire Universe."

    Quantum Mechanics (QM) and Gravity theory (GR) are both needed to address Cosmology. But they are logically diametric or opposite in logical form. GR is due to deductive reasoning and QM is due to inductive reasoning. From Aristotel's idea of gravity through Newton to Einstein the deductive process was used until the current almost complete theory of gravity was derived. QM was an induced process engineered by matching QM with know features of an atom. Combining the Bohr atom with Plank theory and Heisenberg uncertainty principal created the bases for current QM. Deductive reasoning for Gravity is due to the principal of Gravity being the start of the endeavor to explain this obvious natural phenomena. OM is not an obvious natural phenomena but the idea of light photon mechanics seems to me makes the atom more understandable. Also QM is profitable because it supports most the new technological we have today compared to 1910 technology.


    A SUT (super unified theory) or TOE (theory of everything) of some type will have to cover GR and QM. So yes; a complete cosmology has to account for the quantum mechanics. But a theory of everything may not be possible so a complete Cosmology may be a false hope - yet the attempt informs science and seems worth it.

    In Big Band theory the universe started as a singularity that transformed itself into the cosmos we live in so everything is related to that singularity - theoretically . The first point in the universe is related all points in the universe today and every point in space today resonates at the same frequency - the quantum resonant frequency. Every point today is the same point in a resonant frequency way. QM tells us the whole universe is in quantum resonance or the universe as a whole has the same zero point frequency. The whole universe idea used in a QM and GR way is the "whole universe" that I refer to and "entire universe" also seems to work

    Science, in a physics context, is mathematical modeling including QM.

    The title of this forum is Cosmology and I want to keep my statements within the definition that the forum uses. With the definition and with the use of logic and evidence everyone can be expected to stay on topic.

    The main thing about Cosmology is explaining GEOMETRY changing over time as it interacts with matter is true, and GR does the job from the Cosmic scale down to about the molecular scale. However a single theory will need to account for, or explain, both GR and QM.

    I understand why you used the word "replaced" but I like the idea of "refined"; like GR refined Newton's theory of gravity.

    Agreed, yet abstract generalities started science but logic and objectivity refined the abstract generalities to the science of objects - or physics. So we do have a history of working logically with abstract generalities if they have some logical relationship to observation.
  6. Aug 15, 2013 #5
    Their are other key sciences involved as well. QFT better deals with relatistic particle interactions in cosmology than QM. High energy particle physics is also useful to understand early universe thermodynamics and symmetry breaking. Its also useful along with chemistry to understand star formation etc.

    As a self taught cosmologist sort of. I found it necessary to also understand all the other related scientific fields.

    A solid definition should include that aspect of cosmology may better prepare a young student who is interested in the field
  7. Aug 15, 2013 #6


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    Hi Clayjay, thanks for the clear answer. I asked what PURPOSE you wanted the definition of "Cosmology" for and your answer makes it very easy to provide a workable one.
    The criterion I see operating here is that what we inquire about and discuss in Cosmo forum is what professional published cosmologists use as model.

    We don't discuss private individual non-professional theories (even though they may be ABOUT the same questions and phenomena as the professional journal articles). This gives us a nice clear definition similar to what I suggested in my first post,#3.
    Practical working definition of Cosmology: Cosmology is what cosmologists do as shown by peer-review journal publications.
    This turns out to work remarkably well. If you want to scan the latest research go here and see what they are talking about.
    Or search for publications by some prominent cosmologist by name like Abe Loeb or David Spergel. A well-chosen paper on arxiv can be a very good way to start a discussion thread.
    Or look up reports from the Planck satellite mission that have cosmology keyword in the title. Various ways like that. Other people will probably help steer you i the right direction.

    Abstract definitions would make it harder to regulate, adjudicate, forum-manage.

    I have no hand in managing things or any more say than anybody else. I'm just telling you the gist of what I've seen for the most part happening.

    Plus, even simpler, you can just ask questions (about standard expansion cosmology) how this and why that and what does that mean. People will try to give you the straight dope based on the standard cosmic model that the mainstream professionals use.
    Last edited: Aug 15, 2013
  8. Aug 16, 2013 #7
    I was recently introduced in this forum to a new word, cosmogony, which I had not heard before. Reading this wiki page about this word leads me to think that cosmogony probably may not be fully discussed here:

  9. Aug 17, 2013 #8
    Cosmogony is by its own definition (Developing a complete theoretical model has implications in both the philosophy of science and epistemology) is interesting yet beyond the context of cosmology. NASA has this definition which seems complete:
    The Study of the Universe:
    Cosmology is the scientific study of the large scale properties of the universe as a whole. It endeavors to use the scientific method to understand the origin, evolution and ultimate fate of the entire Universe. Like any field of science, cosmology involves the formation of theories or hypotheses about the universe which make specific predictions for phenomena that can be tested with observations. Depending on the outcome of the observations, the theories will need to be abandoned, revised or extended to accommodate the data. The prevailing theory about the origin and evolution of our Universe is the so-called Big Bang theory.

    The process of science needs the philosophy of logic and objectivity; however epistemology is not needed because it is included in underlying framework of objective logic.

    In my opinion the Cosmogony context leads thinking away or beyond the cosmology context and I what to discuss the different current Cosmologies logically and objectively. Knowing professional cosmological theories is different than understanding them. The are a large breadth of professional theories to learn to know here but depth of understanding here seems shallow to me. Data and knowledge is informative but understanding requires knowing the context. "Context controls meaning" is cognitively axiomatic. That is simple logic even in a scientific context. Saying cosmology is what cosmologist do is a tautology structure to me and tautologies are uninformative.

    So Tanelorn, would you like to discuss current cosmology theories logically and objectively in a cosmological context? The NASA cosmology context seems a good one. Also this seemed on target and concise:
    Would anyone here like to understand current cosmology better through logical and objective discourse on the topic within the context? The prevailing cosmology is Big Bang but there are others like Multiverse Theory or String Theory and the "quantum gravity" search in quantum mechanics. The outcome I am looking for is what I can learn through the discussion of cosmology. If someone does not have a definition of cosmology a person can not think about cosmology but someone could have tons of data on the subject that the person does not understand.
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