Cosmology Book
I finished Scott Dodelson's "Modern Cosmology" the other day. By finished I of course mean switched from reading the text to reading bold words, headings, figures and final equations.
It is a detailed look at the physics of the standard post big-bang model. Early universe physics appears to be rife with perturbation theory.
eg Let there be some first order scalar or tensor perturbations. What do they do to the stuff? (stuff includes matter, dark matter, and photons)
OR
Let there be some perturbation in the stuff. What does that do to the curvature?
I actually read half of the book, very nearly word for word. Doing this I did learn a couple of things including that scalar and tensor perturbations are completely independent.
The most important lesson I take away from this is that "Cosmology" really is a word without meaning. Or really is that it has a different meaning for everyone.
What I wanted to learn, but didn't was how CMB anisotropies "prove" the existence of Dark Matter. All I found was that if you suppose some non-interacting substance you get lots of smaller perturbations because they can't coalesce via your everyday radiation processes. This is what we see in the angular size spectrum of the CMB, lots more small clumps than matter would make. My naive perspective is that if gravity works differently at large scales a similar situation would arise.
My greatest challenge in becoming a good theorist will be to avoid ad-hoc or lay-sounding "theories". I must learn enough to know what can and cant reasonably be proposed. For example, I don't know enough about current ideas in quantum gravity to avoid thinking that maybe the gravity quanta have a decay lifetime, so that if there are large distances between the attractors the quanta could decay into somethings that interact differently. This would explain the sharp diversion point from Newtonian physics in the rotational curves of many spiral galaxies.
It is a detailed look at the physics of the standard post big-bang model. Early universe physics appears to be rife with perturbation theory.
eg Let there be some first order scalar or tensor perturbations. What do they do to the stuff? (stuff includes matter, dark matter, and photons)
OR
Let there be some perturbation in the stuff. What does that do to the curvature?
I actually read half of the book, very nearly word for word. Doing this I did learn a couple of things including that scalar and tensor perturbations are completely independent.
The most important lesson I take away from this is that "Cosmology" really is a word without meaning. Or really is that it has a different meaning for everyone.
What I wanted to learn, but didn't was how CMB anisotropies "prove" the existence of Dark Matter. All I found was that if you suppose some non-interacting substance you get lots of smaller perturbations because they can't coalesce via your everyday radiation processes. This is what we see in the angular size spectrum of the CMB, lots more small clumps than matter would make. My naive perspective is that if gravity works differently at large scales a similar situation would arise.
My greatest challenge in becoming a good theorist will be to avoid ad-hoc or lay-sounding "theories". I must learn enough to know what can and cant reasonably be proposed. For example, I don't know enough about current ideas in quantum gravity to avoid thinking that maybe the gravity quanta have a decay lifetime, so that if there are large distances between the attractors the quanta could decay into somethings that interact differently. This would explain the sharp diversion point from Newtonian physics in the rotational curves of many spiral galaxies.
Labels: Readings
posted by Danny at 10:51 AM
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