The one (listed under other problems) which always struck me since the first time I heard it:
"How does the quantum description of reality, which includes elements such as the superposition of states and wavefunction collapse or quantum decoherence, give rise to the reality we perceive? "<p>I still vividly remember the first time I heard the "collapse of the wavefunction" and openly challenged our poor Solid-state electronics professor - it led to a looong discussion at the end of which he got flustered enough that after shifting thru entanglement, decoherence, Measurement problems, many worlds interpretation, Bohm, time travelling interactions, philosophy, etc he pretty much kicked me out of his office.<p>I think I might have partly contributed to him seeking a transfer to another dept. the next year...
I always find reading over this article pretty entertaining, in particular Sonoluminescence generally catches my attention:<p><a href="http://en.wikipedia.org/wiki/Sonoluminescence" rel="nofollow">http://en.wikipedia.org/wiki/Sonoluminescence</a><p>As it seems like it should be practical to replicate it on a relatively small budget.
"Ecliptic alignment of CMB anisotropy<p>Some large features of the microwave sky at distances of over 13 billion light years appear to be aligned with both the motion and orientation of the solar system. Is this due to systematic errors in processing, contamination of results by local effects, or an unexplained violation of the Copernican principle?"<p>Wait what? An unexplained violation of the Copernican principle? That's pretty crazy. What is being referred to? The article on the CMB says that it's isotropic to one part in a thousand
The list of unsolved problems by field <a href="http://en.wikipedia.org/wiki/Lists_of_unsolved_problems" rel="nofollow">http://en.wikipedia.org/wiki/Lists_of_unsolved_problems</a>
Reading through these makes me really miss my undergraduate days as a physics major.<p>Only marginally related:
If you ever have a chance to go to one of the LIGO [1] sites (Laser Interferometer Gravitational-wave Observatory), do go take a tour! I've been to the one in Livingston, Louisiana [2], and it is simply amazing. The technology used and the science involved is very interesting. It's also kid-friendly!<p>[1] <a href="http://www.ligo.caltech.edu/" rel="nofollow">http://www.ligo.caltech.edu/</a>
[2] <a href="http://www.ligo-la.caltech.edu/" rel="nofollow">http://www.ligo-la.caltech.edu/</a>
It's been a while since my physics degree but aren't the "cosmological constant problem" and the "vacuum catastrophe" two different phrasings for the same problem? reading through to the linked pages doesn't help me in understanding what the difference between the two is (or if there is any).
> The beauty and clearness of the dynamical theory, which asserts heat and light to be modes of motion, is at present obscured by two clouds.<p>Lord Kelvin's two clouds led us to relativity and quantum mechanics.
"Whats a Z job?"
"If you have to ask you can't afford it"
-Beerfest<p>"What are some unsolved physics problems?"
"If you have to ask you can't solve them"
-spanko