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Resources

Below you will find links and suggested reading on various topics and at the beginning of each section a list of FAQ's (Frequently Asked Questions) that I have either received from others or that I have pondered at some point myself. If you would like to submit a question please do so [ here ].

Topics (Suggestions welcome)

General Physics
Superstring Theory
Cosmology
General Relativity

General Physics

FAQs

Can Theoretical Physics explain paranormal phenomena?
[Answer courtesy: Nobel Laureate Gerald t'Hooft]
What if all things can't be explained using physics?
This is certainly a possibility, however, if physics and mathematics is inadequate to describe reality, that only leaves a realm that would be useless for us to know anyway. Besides "to know" means to apply a logical system to describe something, if mathematics (logic) is not applicable what else would one use? Faith is not an alternative to logic, for it is based on logic. One could define faith as the group of prejudices established by one to avoid reason.
What is theoretical physics?
[see this page] (answer provided by The Official String Theory Website)

Suggested Reading

The Elegant Universe, Brian Greene (popular introduction)
String Theory: An Introduction to the Bosonic String, Joseph Polchinski (advanced)

Cosmology

FAQs

Confession: This is not the best place for FAQs on cosmology, this place is [click here]. Ned Wright has put together an incredible list of FAQs regarding cosmology and astronomy. I have posted a few questions on my site and would be happy to answer questions, but his site is incredible!

I visualize the universe as starting with the big bang at some point source
and expanding to this date. This must not be correct because we could not
see light from objects 10 billion light years away. That light should be
long past us. I do not know how we can see light from objects that far from
us. Please explain. This has bothered me for years.
As the universe expands from the initial point the distances between the points also expands. Since the speed of light is finite and the distance between points in the universe is increasing, that means that a lot of the universe is still invisible to us (outside our light cone). However, I think the point that is confusing you is this: When we say an object is 10 Billion light years away, this does not mean that its distance is exactly distance= 10 Billion Lyr * speed of light. Why not? Because as the universe expands the way to measure time and distance changes. Light traveling from a source 10 Billion Lyr away TODAY, is not the same distance away as it was 10 Billion YEARS ago, since the distance between us and them is continually increasing.

Let us look at it from another point of view: Say we send out a radio signal to aliens today and hope to reach a galaxy 10 Billion Lyr away. As the light (radio wave) travels through space, space itself is expanding. The aliens are 10 Billion Lyr away today, but by the time the signal reaches them the universe will be much, much larger.

So the point is, as light travels at finite speed the universe continues to expand, making light travel farther and farther. Imagine running a race on a track that expanded as you ran. Of course, if the track expanded faster than you ran you would never get there. Luckily this is not the case!
Is the redshift we observe in faraway galaxies (from which we derive the Hubble constant) caused by the expansion of space-time; or is it simply due to the fact that those galaxies are receding from us at high speed, and therefore are exhibiting a Doppler redshift? Or is there some mixture of the two? [abridged]
The Hubble constant is derived from the expansion of space-time. Between our galaxy and say, some other galaxy many hundreds of light years away, the effect of space-time expanding can be seen in the Hubble law and the "cooling", i.e., red shifting of the Cosmic Microwave Background. For large distances this "red shifting" dominates the others (Doppler effects). The average velocity of galaxies within clusters is ~300 K/Pc, which is minute compared with the overall expansion of space-time (on large scales). So, to answer your question, over large distances (the scale of cosmology) we can ignore all redshift phenomena except the "Hubble Expansion", which yields the "stretching" of the CMB and the Hubble Law.
What is the cosmological constant?
Quantum Field Theory (QFT) predicts the existence of an energy for the vacuum. That's right! The vacuum is not empty. This can be understood in terms of the Heisenberg uncertainty principle, which tells us that the quantum vacuum is always undergoing violent fluctuations in energy. The expectation (or average) values of this vacuum energy are termed the Cosmological constant. This constant was originally invoked by Einstein to make his equations predict a static universe. However, today this constant is interpreted as causing an accelerating universe. Two of the most investigated questions in all of physics are based on this constant. QFT predicts a value 122 orders of magnitude greater than experiment measures. Second, observations suggest that the vacuum energy NOW represents 70% of all the energy of the universe and is controlling the expansion rate, why now? [More from the MAP homepage]
What is the theory of Inflation?
Inflation is simply a model of cosmology that suggests particle physics consideration in the early universe resulted in a brief period of exponential (faster than light) expansion. For a more in depth review please consult my online introduction [here].
What is the Big Bang?
[Answer courtesy MAP homepage]
How old is the universe?
[Answer courtesy MAP homepage]
How fast is the universe expanding?
[Answer courtesy MAP homepage]
Is the universe infinite?
[Answer courtesy MAP homepage]
What is the universe made of?
[Answer courtesy MAP homepage]
How did the chemical elements form?
[Answer courtesy MAP homepage]
How did galaxies and large scale structure form in the early universe?
[Answer courtesy MAP homepage]
What is the cosmic microwave background radiation?
[Answer courtesy MAP homepage]
What are cosmic microwave background fluctuations?
[Answer courtesy MAP homepage]
What is the Milky Way?
[Answer courtesy MAP homepage]

Current satellite-based CMB observatories:

COBE, spectrum and anisotropy, NASA/Goddard

Future satellite-based CMB observatories:

Current balloon and ground-based CMB anisotropy experiments:

Future balloon and ground-based CMB anisotropy experiments:

Sites for CMB Theory and Analysis:

Sites for CMB Software:

Large Scale Structure Surveys

Planck Project Related Sites

Cambridge Planck Analysis Centre (CPAC)
Max-Planck-Institut für Astrophysik Planck Analysis Centre (MPAC)
Cosmic Microwave Background Network in Europe for Theory and data analysis (or, mercifully, CMBNET)
Document Management System (DMS; password required)
ESTEC Livelink (password required)
Integrated Data and Information System (IDIS; password or host access required)
Planck Surveyor (European Space Agency site)