Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Working in the field of cosmolg

  1. Nov 10, 2004 #1
    I have spent about four year of my research (ph.d) working in the field of cosmolgy. I like it very much and I want to do something interesting.
    My problem is that I do not have a good communication with my supervisor and some time we do not communicate for a long time at all. I am afraid of asking questions, I have the impression that if I ask something he will get angry. Most of the time I dot understand what he says. I have clear idea that what we are doing is not significant at all (actually we are not doing anything coherent, some time we pick a problem and without finishing that we leave that and jump on next and so on .. so far we have published a paper but that is in arXiv only). Right now the place at which I am working has very good infrastructure but there are almost no other people in astro or cosmology to whom I can talk. I am thinking of two options.
    (1). I have to keep patience and study myself (because I am hardly been supervised so I have plenty of time) and go ahead.
    (2) I have to try for some other place, this will essentially push me for GRE and I have to spend more number of years to get a phd. If I chose the first option then there is a chance that I will get a phd, but after that I will not have too many options due to my poor research.
    If I chose the second option then there is chance of having bright future but before that I have to spend a lot of time, money and efforts to get a place.
    Plese suggest me what I should do
    Last edited: Nov 10, 2004
  2. jcsd
  3. Nov 10, 2004 #2


    User Avatar
    Science Advisor
    Gold Member

    I think your mentor is looking for you to take an interest in something and go after it with a passion. Do not be afraid of being wrong, be afraid of never taking a chance.
  4. Nov 10, 2004 #3


    User Avatar
    Science Advisor
    Gold Member

    cosmoboy - Chronos advice is right; what problems within cosmology have you been looking at?

  5. Nov 10, 2004 #4
    I am looking at the structure formation in the universe. This work is mostly computational. we use N-body simulation.
  6. Nov 11, 2004 #5


    User Avatar
    Science Advisor
    Gold Member

    So show some passion for your research! Your mentor, who is very busy, will never care more about your project than you do. Just friendly advice, cosmo. When you go pester the mentor with your problems be well enough prepared to expect and have an answer to the obvious questions you will be asked. Having been there as an instructor, I guarantee I spent a lot more time helping people solve problems I never expected them to be able to solve on their own. Even old people still enjoy learning new things and it sparks their curiousity.

    ps: I hold Garth in the highest regard. He is very familiar and knowlegeable in matters such as those you have an interest in. He is also very patient with people like us who are still groping in the dark to find the pinata.
    Last edited: Nov 11, 2004
  7. Nov 11, 2004 #6


    User Avatar
    Science Advisor
    Gold Member

    cosmoboy - are you looking for a definite and coherent project to get your teeth into?
  8. Nov 11, 2004 #7

    yes, indeed.

    I am thankful to all of you for the support I am getting.

    Ambitwistor is sending me really very good advice but they are coming in private messages. Some how I some time I am able and some time not to reply him. I am new to this forum so I do not know what is happening.

    best wishes
    Last edited: Nov 11, 2004
  9. Nov 12, 2004 #8


    User Avatar
    Science Advisor
    Gold Member

    As a project I would suggest looking at structure formation in the "freely coasting universe". One in which R(t) = t strictly from t = 0 until the present day.
    Some papers to get you going if interested:
    A “Freely Coasting” Universe http://arxiv.org/abs/astro-ph/0209209
    The New Interpretation of the Uniformly Expanding Universe http://arxiv.org/abs/astro-ph/0408519

    and: "Self Creation Cosmology - An Alternative Gravitational Theory" http://arxiv.org/abs/gr-qc/0405094

    I hope you find this helpful,

  10. Nov 12, 2004 #9
    I have looked at the above articles. I found these interesting but they are slighly off from my track .

    Since now we are becoming involved in this discussion so let me put a brief history of the study of structure formation in the universe. This will help me to summarize my understanding and for others it might give a glimpse of this field.

    History of this problem goes back to 1902 when Jeans proved that for any cloud massive than the Jenas mass will eventually collapse, because for such a large cloud pressure forces are not able to support it against gravitational collapse. In 1948 Gamow put forwared an idea of galaxy formation in the universe by gravitational instability.

    One can start the journey of this problem from the Peebles's 1967 paper http://adsabs.harvard.edu/cgi-bin/n...J...147..859P&db_key=AST&high=3f8b9c6d4511183

    In this this paper many important references are given and it is argued that an expanding universe is unstable to gravitational perturbation and this instability could lead structure formation in the universe. One of the important works which was already known at that time was the cosmological perturbation theory of Lifstiz.

    In 1967 D. Lyden-Bell http://adsabs.harvard.edu/cgi-bin/n...RAS.136..101L&db_key=AST&high=3f8b9c6d4509860
    argued that the violently changing gravitational field of a newly formed galaxy is effective in changig the statistic of stellar orbits. There have been many implications of this idea. Even at that time it was clear that if we begin with a homogeneous and isotropic expanding universe we could get structures if we slightly perturb the matter field. Mathematical equations for density perturbation and velocity perturbation were written down and first order perturbation theory was applied. This approch was quite satisfactory for small perturbations but for large perturbations it failed because the evolution equations became second order coupled non linear partial differntial equations and there was no solution available. Some progress was made when the Russian physicist Zeldovich proposed a new approximation schme
    In this approximation Lagrangian coordinate system was used which was quite effective in representing non-linearity.

    Peebles 1974's paper
    is one of the important landmarks. In this paper equations for the the evolution of density contrast were derived and it was argued that as longs as density perturbations are small their various fourier modes evolve independently but when these become large they start to couple with each other.

    In 1974 Press & Schecter shown that fraction of mass in haloes
    more massive than M is related to the fraction of volume in which the smooth initial density field is above some threshold. They derived an important relation for mass function considering initial field as a gaussian random.

    In 1977 Davis & Peebles published a long paper in Apj which systematically started this study. They derived many important relations for n-point correlation functions. After that n-point correlation functions became an important tool to understand this problem
    These n-point correlation functions are discussed in a great depth in Peebles's 1981 classic book "The large scale structure of the Universe".

    For the last few decade cosmological n-body simulations have become important tolls to understand this problem http://adsabs.harvard.edu/cgi-bin/n...J...292..371D&db_key=AST&high=3f8b9c6d4512670

    N-body technique are discussed in a great detail in this paper

    A lot of work has been done by Barden et al. http://adsabs.harvard.edu/cgi-bin/n...J...304...15B&db_key=AST&high=3f8b9c6d4512916
    B Jain & Bertschinger

    There are many good review articles on this problem but the following 309 page long physics report covers cosmological perturbation theory in a great detail and gives many important references http://arxiv.org/abs/astro-ph/0112551

    Let me finish by summarizing what I am interested in
    1. the model independent understanding of structure formation in the universe
    2. statistical mechanics of gravitating n body system
    3 cosmological simulations involving gas and/or radiation physics
    4. constraining the topology of universe by observing large scale structures
    5. generation of perturbation in inflationary regime
    6 constraining primordial power spectrum (cosmological initial condition)
    7. constraining cosmological parameters

    These are a few areas which I want to explore, although I am not working on anyone of them

    There is a very good book on the unsolved problems in physics if anybody has not looked it visit here

    write your views about the above problems

    best wishes
    Last edited: Nov 13, 2004
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook